b Series 3 6 al - manuals.decagon.commanuals.decagon.com/Retired and Discontinued... · AquaLab Lab...

Wat

er A

ctiv

ity

Met

er

Op

erat

or’s

Man

ual

Vers

ion

6

for

Aq

uaL

ab S

erie

s 3

Dec

agon

Dev

ices

, In

c.

Decagon

Devices, In

c.2365 N

E H

opkins CourtPullm

an WA

99163(509) 332-2756

fax: (509) 332-5158w

ww.decagon.com

[email protected]

Trademarks

AquaLab is a registered tradem

ark of D

ecagon Devices, Inc.

© 1990-2009 D

ecagon Devices, Inc.

Aqu

aLab

Tabl

e of

Con

tent

s

i

Co

nten

ts1.

Int

rod

ucti

on

. . .

. . .

. . .

. . .

. . .

. . .

. . 1

Abo

ut th

is M

anua

l .

. . .

. . .

. . .

. . .

. . .

. . .

. 1

Cus

tom

er S

uppo

rt .

. . .

. . .

. . .

. . .

. . .

. . .

. . 1

War

rant

y . .

. . .

. . .

. . .

. . .

. . .

. . .

. . .

. . .

. .2

Selle

r’s

Liab

ility

. . .

. . .

. . .

. . .

. . .

. . .

. . .

. .3

2. A

bo

ut A

qua

Lab

. .

. . .

. . .

. . .

. . .

. . .

4A

quaL

ab 3

Inst

rum

ent S

peci

ficat

ions

. .

. .4

Aqu

aLab

and

Wat

er A

ctiv

ity .

. . .

. . .

. . .

.5

How

Aqu

aLab

wor

ks .

. . .

. . .

. . .

. . .

. . .

. .5

Aqu

aLab

and

Tem

pera

ture

. .

. . .

. . .

. . .

. .6

Lim

itatio

ns .

. . .

. . .

. . .

. . .

. . .

. . .

. . .

. . .

. . .

8

3. W

ate

r A

ctiv

ity

The

ory

. .

. . .

. . .

. . .

9M

oist

ure

cont

ent

. . .

. . .

. . .

. . .

. . .

. . .

. . .

.9W

ater

act

ivity

. . .

. . .

. . .

. . .

. . .

. . .

. . .

. . .

9Te

mpe

ratu

re E

ffec

ts .

. . .

. . .

. . .

. . .

. . .

. . .

11W

ater

Pot

entia

l . .

. . .

. . .

. . .

. . .

. . .

. . .

. . 1

2Fa

ctor

s in

Det

erm

inin

g W

ater

Pot

entia

l . 1

3So

rptio

n Is

othe

rms

. . .

. . .

. . .

. . .

. . .

. . .

. 15

4. G

etti

ng S

tart

ed .

. . .

. . .

. . .

. . .

. . .

17

Com

pone

nts

of y

our

Aqu

aLab

. .

. . .

. . .

. 17

Cho

osin

g a

Loca

tion

. . .

. . .

. . .

. . .

. . .

. . .

17Fe

atur

es

. . .

. . .

. . .

. . .

. . .

. . .

. . .

. . .

. . .

. 18

Prep

arin

g A

quaL

ab f

or O

pera

tion

. . .

. . 1

9

5. T

he M

enus

. .

. . .

. . .

. . .

. . .

. . .

. . .

21

The

Mea

sure

men

t Scr

een

. . .

. . .

. . .

. . .

. 21

AquaLab

Index

100

Troubleshooting 54

VVerification 35

Verification standards 33

aw readings too high/

low for 57

compared to saturated salts 91

Volatiles 8, 46

WWarm

-up 20W

arranty 2W

ater activityadjusting for offset 39A

qualab and 4calibration standards 34definition 5, 9displayed 19effect on food 5, 9low

50, 51stability diagram 10theory 9

Water contentdefinition 9vs. w

ater activity 9W

ater potentialfactors in determ

ining 13m

atric effects 14osm

otic effects 13relation to w

ater activity 12

AquaLab

Table of Contents

ii

Changing Languages . . . . . . . . . . . . . . . . . . 21

Norm

al Sampling M

ode . . . . . . . . . . . . . . .22C

ontinuous Mode . . . . . . . . . . . . . . . . . . . .23

Temperature Equilibration Screen . . . . . .23

System C

onfiguration . . . . . . . . . . . . . . . . .24

6. Clea

ning a

nd M

aintena

nce . . . . . . .27

Cleaning the Block and Sensors . . . . . . . .28

Cleaning Procedure: . . . . . . . . . . . . . . . . . .29

Checking C

alibration . . . . . . . . . . . . . . . . .32

7. V

erificatio

n and

Ca

libra

tion . . . . . .3

3W

ater Activity V

erification . . . . . . . . . . .33C

alibration Standards . . . . . . . . . . . . . . . .33C

alibration . . . . . . . . . . . . . . . . . . . . . . . . . .35

8. Sam

ple Prep

ara

tion . . . . . . . . . . . .4

1Preparing the Sam

ple . . . . . . . . . . . . . . . . . 41Sam

ples Needing Special Preparation . .43

Low W

ater Activity . . . . . . . . . . . . . . . . . .46

9. Ta

king

a R

ead

ing . . . . . . . . . . . . . .4

8M

easurement Steps . . . . . . . . . . . . . . . . . .48

How

AquaLab takes Readings . . . . . . . . .49

Cautions . . . . . . . . . . . . . . . . . . . . . . . . . . . .49

10. Co

mp

uter Interface . . . . . . . . . . . .52

AquaLink Softw

are . . . . . . . . . . . . . . . . . . .52Using W

indows H

yperterminal . . . . . . . . .53

11. Troub

leshoo

ting . . . . . . . . . . . . . . .54

Com

ponent Performance Screen . . . . . . .62

Aqu

aLab

Inde

x

99

dehy

drat

ed 4

4dr

ied

43lo

w w

ater

act

ivity

46

mult

i-com

pone

nt 4

1ne

edin

g sp

ecia

l pre

para

tion

43no

t at r

oom

tem

pera

ture

46

slow

wat

er-e

mitt

ing

44su

rface

are

a of

44

visc

ous 4

4Sa

mpl

ing

mod

esco

ntin

uous

23

norm

al 2

1Sa

tura

ted

salts

90

Selle

r’s

liabi

lity

3Sp

anis

h 21

Spill

ing

the

sam

ple

49Sw

edis

h 21

T Tech

nica

l sup

port

1Te

mpe

ratu

reef

fect

s on

wat

er a

ctiv

ity 1

1ho

t sam

ples

50

of in

stru

men

t 50

sam

ples

not

at r

oom

tem

p. 4

6Te

mpe

ratu

re c

ontr

ol 6

reas

ons

for 7

Theo

ryw

ater

act

ivity

67

Tim

e long

read

tim

es 5

6Tr

iang

lem

irror

per

form

ance

indi

cato

r 60

Aqu

aLab

Tabl

e of

Con

tent

s

iii

12. S

upp

ort

and

Rep

air

.

. . .

. . .

. . .

.64

Ship

ping

Dir

ectio

ns:

. . .

. . .

. . .

. . .

. . .

. . .6

4Re

pair

Cos

ts .

. . .

. . .

. . .

. . .

. . .

. . .

. . .

. . .6

6Lo

aner

Ser

vice

. .

. . .

. . .

. . .

. . .

. . .

. . .

. .6

6

13. F

urth

er R

ead

ing

. .

. . .

. . .

. . .

. . .

.67

Wat

er A

ctiv

ity T

heor

y &

Mea

sure

men

t 67

Food

Qua

lity

and

Safe

ty .

. . .

. . .

. . .

. . .

. 71

Wat

er A

ctiv

ity a

nd M

icro

biol

ogy

. . .

. . .7

3W

ater

Act

ivity

in F

oods

. .

. . .

. . .

. . .

. . .

77Ph

arm

aceu

tical

s/C

osm

etic

s .

. . .

. . .

. . .

.86

Mis

cella

neou

s .

. . .

. . .

. . .

. . .

. . .

. . .

. . .

.88

Ap

pen

dix

A .

. . .

. . .

. . .

. . .

. . .

. . .

. .9

0Pr

epar

ing

Salt

Solu

tion

. . .

. . .

. . .

. . .

. . .

90

Ap

pen

dix

B

. . .

. . .

. . .

. . .

. . .

. . .

. . .

92

Dec

lara

tio

n o

f Co

nfo

rmit

y .

. . .

. . .

. .9

3

Cert

ific

ate

of

Tra

cea

bil

ity

. .

. . .

. . .

.9

4

AquaLab

Index

98

PPeltier cooler 6Portuguese 21Preparing salt solutions 90Propylene glycol 46, 56

cleaning out of chamber 46

RRead time

affected by sample tem

p. 46long read tim

e 6, 43, 56Readings

cautions 49how

AquaLab takes 48, 49

taking readings 48References 67Relative hum

idity 5, 11Repair

instructions for 64

SSalt standards. See calibration standardsSam

pleslow

water-em

itting 56Sam

ple cupscleaning 42filling level 42

Sample equilibration screen 7

Sample preparation 41

Sample too dry 51, 58, 59

Sample too hot 47, 50

Samples

coated 43

AquaLab

1. Introduction

1

1. Introd

uction

Welcom

e to Decagon’s A

qu

aLab

Series 3, the industry standard for m

easuring water activity (aw ). A

quaLab is the quickest, m

ost accurate, and most reliable instrum

ent available for m

easuring water activity. W

hether you are doing

research or

working on

the production

line, A

quaLab will suit your needs. It is easy to use and pro-

vides accurate and timely results. W

e hope you find this m

anual informative and helpful in understanding how

to m

aximize the capabilities of your A

quaLab.

Ab

out this M

anua

lIncluded in this m

anual are instructions for setting up your A

quaLab, verifying the calibration of the instrument,

preparing samples, and m

aintaining and caring for your instrum

ent. Please read these instructions before operat-ing A

quaLab to ensure that the instrument perform

s to its full potential.

Custo

mer Sup

po

rtIf you ever need assistance w

ith your AquaLab, or if you

just have questions, there are several ways to contact us:

NO

TE: If you purchased your A

quaLab through a distributor, please contact them for assistance.

Aqu

aLab

Inde

x

97

I Italia

n 21

L Lang

uage

sch

angi

ng 2

1LE

D 2

5Li

near

off

set

caus

es fo

r 33

defin

ition

33

how

to a

djus

t for

35

men

u 26

whe

n to

ver

ify fo

r 35

Loca

tion

for s

ampl

ing

18Lo

w w

ater

act

ivity

46,

50

M Mai

n m

enu

19, 2

1M

aint

enan

ce 2

7M

anua

l 1M

ater

ial S

afet

y D

ata

Shee

t 34

Men

us mai

n m

enu

21sy

stem

con

figur

atio

n 24

N NIS

T trace

abili

ty 9

4N

orw

egia

n 21

O Osm

otic

eff

ects

13

Aqu

aLab

1. Int

rodu

ctio

n

2

E-m

ail

sup

por

t@d

ecag

on.c

omPl

ease

inc

lude

you

r na

me,

cont

act

info

rmat

ion,

ins

tru-

men

t ser

ial n

umbe

r(s),

and

a de

scrip

tion

of y

our p

robl

em

or q

uest

ion.

sale

s@d

ecag

on.c

omPl

ease

inc

lude

you

r na

me,

addr

ess,

phon

e nu

mbe

r, th

e ite

ms

you

wish

to

orde

r an

d a

purc

hase

ord

er n

umbe

r. Cr

edit

card

num

bers

shou

ld a

lway

s be

calle

d in

.

Phon

e1-

800-

755-

2751

(USA

and

Can

ada

Onl

y)1-

509-

332-

2756

(Int

erna

tiona

l)

Our

Cus

tom

er S

uppo

rt an

d Sa

les R

epre

sent

ativ

es a

re

avail

able

Mon

day

thru

Frid

ay.

Fax

1-50

9-33

2-51

58

Wa

rra

nty

Aqu

aLab

has

a 3

0-da

y sa

tisfa

ctio

n gu

aran

tee

and

a th

ree-

year

war

rant

y on

par

ts a

nd la

bor.

Your

war

rant

y is

auto

-m

atica

lly v

alida

ted

upon

rece

ipt o

f the

inst

rum

ent.

We

will

co

ntac

t yo

u w

ithin

the

firs

t 90

day

s of

you

r pu

rcha

se t

o se

e ho

w th

e A

quaL

ab is

wor

king

for y

ou.

AquaLab

Index

96

Continuous sam

pling mode 23

Custom

er service 1C

zech 21

DDanish 21

Declaration of C

onformity 93

Dehydrated sam

ples 44D

ried samples 43

Dry sam

ples 50, 58, 59

EError messages 54

"sample too dry" 58, 59

"sample too hot" 58

triangle on screen 60Exit 26

FFaninside sample cham

ber 6Features 18Flashing. See LEDFrench 21Further reading 67Fuse, changing of 55

GGerm

an 21

HHyperterm

inalusing for dow

nloading 53

AquaLab

1. Introduction

3

Seller’s Liab

ilitySeller w

arrants new equipm

ent of its own m

anufacture against defective workm

anship and materials for a period

of three years from date of receipt of equipm

ent (the results of ordinary w

ear and tear, neglect, misuse, accident

and excessive deterioration due to corrosion from any

cause are not to be considered a defect); but Seller’s liabil -ity for defective parts shall in no event exceed the furnish-ing of replacem

ent parts Freight on Board the factory w

here originally manufactured. M

aterial and equipment

covered hereby which is not m

anufactured by Seller shall be covered only by the w

arranty of its manufacturer. Seller

shall not be liable to Buyer for loss, damage or injuries to

persons (including death), or to property or things of w

hatsoever kind (including, but not without lim

itation, loss of anticipated profits), occasioned by or arising out of the installation, operation, use, m

isuse, nonuse, repair, or replacem

ent of said material and equipm

ent, or out of the use of any m

ethod or process for which the sam

e may be

employed. The use of this equipm

ent constitutes Buyer’s acceptance of the term

s set forth in this warranty. There

are no understandings, representations, or warranties of

any kind, express, implied, statutory or otherw

ise (includ-ing, but w

ithout limitation, the im

plied warranties of m

er-chantability and fitness for a particular purpose), not expressly set forth herein.

Aqu

aLab

Inde

x

95

Inde

xA A

cces

sori

es 1

7A

ccur

acy

4A

quaL

aban

d ch

illed

mirr

or d

ewpo

int t

echn

ique

5an

d te

mpe

ratu

re 6

limita

tions

of 8

theo

ry 9

B Beep

er 2

5ch

angi

ngBl

ock

failu

re 6

1Bu

tton

sfo

r lin

ear o

ffset

set

tings

37

for m

enu

sele

ctio

n 21

C C f

or c

ontin

uous

mod

e 23

Cal

ibra

tion

35C

alib

ratio

n st

anda

rds 3

3C

autio

ns 4

9C

E co

mpl

ianc

e 93

Chi

lled-

mir

ror

tech

niqu

e 5

Cle

anin

g 27

Coa

ted

sam

ples

shor

teni

ng re

ad ti

me

for 4

3C

ompo

nent

per

form

ance

indi

cato

r 62

Com

pone

nts

17C

ompu

ter

inte

rfac

e 52

Aqu

aLab

2. A

bout

Aqu

aLab

4

2. A

bo

ut A

qua

Lab

Aqu

aLab

is

the

quick

est

and

mos

t ac

cura

te i

nstr

umen

t av

ailab

le fo

r m

easu

ring

wat

er a

ctiv

ity, g

ivin

g re

adin

gs in

fiv

e m

inut

es o

r les

s. Its

read

ings

are

the

mos

t reli

able

pro-

vidi

ng ±

0.00

3aw a

ccur

acy.

The

inst

rum

ent i

s ea

sy to

clea

n an

d ch

ecki

ng c

alibr

atio

n is

simpl

e.

Aqu

aLab

3 In

stru

men

t Sp

ecif

icat

ions

Wat

er A

ctiv

ity

Ran

ge:

0.03

0 to

1.0

00W

ater

Act

ivit

y A

ccu

racy

: ±

0.00

3W

ater

Act

ivit

y R

esol

uti

on:

±0.

001

Rea

d t

ime1 :

< 5

min

.Sa

mp

le T

emp

erat

ure

Ran

ge:

15 to

50°

CSa

mp

le T

emp

erat

ure

acc

ura

cy2 :

±0.

2° C

Sam

ple

Tem

per

atu

re r

esol

uti

on:

0.1°

CSa

mp

le D

ish

Cap

acit

y: 7

ml r

ecom

men

ded

(15

ml f

ull)

Op

erat

ing

Env

iron

men

t: 4

to 5

0° C

;

0 to

90%

Rela

tive H

umid

ity (n

on-c

onde

nsin

g)C

ase

Dim

ensi

ons:

24.

1 x

22.9

x 8

.9 c

mW

eigh

t: 3

.2 K

gC

ase

Mat

eria

l: P

owde

r Pain

ted

Alu

min

umD

isp

lay:

20

x 2

alpha

num

eric

LCD

with

bac

klig

htin

gD

ata

Com

mu

nic

atio

n:

RS23

2A c

ompa

tible,

8-d

ata

bit

ASC

II c

ode,

9600

bau

d, n

o pa

rity,

1 st

op b

itP

ower

: 11

0VAC

to 2

20 V

AC, 5

0/60

Hz

War

ran

ty:

3 ye

ar p

arts

and

labo

r

AquaLab

Certificate of Traceability

94

Certificate of Traceability

Decagon D

evices, Inc.2365 N

E Hopkins C

ourtPullm

an WA

99163tel: (509) 332-2756fax: (509) 332-5158

[email protected]

This is to certify that AquaLab w

ater activity meters are

manufactured utilizing tem

perature standards with calibra-

tion traceable to the National Institute of Standards and

Technology (NIST).

AquaLab

2. About A

quaLab

5

1on samples w

ith no significant impedance to vapor loss

2AquaLab is calibrated to a N

IST traceable temperature

standard.

Aq

uaLa

b a

nd W

ater A

ctivity

Water activity (aw ) is a m

easurement of the energy status

of the water in a system

. It indicates how tightly w

ater is “bound”, structurally or chem

ically, within a substance.

Water activity is the relative hum

idity of air in equilibrium

with a sam

ple in a sealed measurem

ent chamber. The con-

cept of water activity is of particular im

portance in deter-m

ining product

quality and

safety. W

ater activity

influences color, odor, flavor, texture and shelf-life of m

any products. It predicts safety and stability with respect

to microbial grow

th, chemical and biochem

ical reaction rates, and physical properties. For a m

ore detailed descrip-tion of w

ater activity as it pertains to products, please refer to Chpt. 3 of this m

anual, titled “Water A

ctivity Theory”.

Ho

w A

qua

Lab

wo

rks

AquaLab uses the chilled-m

irror dewpoint technique to

measure the w

ater activity of a sample. In an instrum

ent that uses the dew

point technique, the sample is equili-

brated with the headspace of a sealed cham

ber that con-tains a m

irror and a means of detecting condensation on

the mirror. A

t equilibrium, the relative hum

idity of the air in the cham

ber is the same as the w

ater activity of the sam

ple. In the AquaLab, the m

irror temperature is pre -

Aqu

aLab

Decl

arat

ion o

f Con

form

ity

93

Dec

lara

tion

of

Con

form

ity

App

licat

ion

of C

ounc

il 89

/336

/EE

CD

irect

ive:

Stan

dard

s to

whi

ch

EN

81-1

co

nfor

mity

is d

eclar

ed:

EN

5000

82-1

Man

ufac

ture

r’s N

ame:

Dec

agon

Dev

ices,

Inc.

2365

NE

Hop

kins

Cou

rtPu

llman

, WA

991

63U

SA

Type

of E

quip

men

t:A

quaL

ab w

ater

activ

ity m

eter

.

Mod

el N

umbe

r:Se

ries 3

Year

of F

irst M

anuf

actu

re:

1999

This

is to

cer

tify

that

the

Aqu

aLab

wat

er a

ctiv

ity m

eter

, m

anuf

actu

red

by D

ecag

on D

evice

s, In

c., a

cor

pora

tion

base

d in

Pul

lman

, Was

hing

ton,

USA

mee

ts o

r exc

eeds

the

stan

dard

s for

CE

com

plian

ce a

s per

the

Coun

cil D

irec-

tives

not

ed a

bove

. All

inst

rum

ents

are

bui

lt at

the

fact

ory

at D

ecag

on a

nd p

ertin

ent t

estin

g do

cum

enta

tion

is fr

eely

avail

able

for v

erica

tion.

Thi

s cer

tifica

tion

appl

ies to

all

Aqu

aLab

Ser

ies 3

mod

els, i

nclu

ding

, but

not

lim

ited

to,

the

Serie

s 3 a

nd 3

TE.

Aqu

aLab

2. A

bout

Aqu

aLab

6

cisely

co

ntro

lled

by

a th

erm

oelec

tric

(Pelt

ier)

cool

er.

Det

ectio

n of

the

exac

t poi

nt a

t whi

ch c

onde

nsat

ion

first

ap

pear

s on

the

mirr

or i

s ob

serv

ed w

ith a

pho

toele

ctric

ce

ll. A

bea

m o

f lig

ht i

s di

rect

ed o

nto

the

mirr

or a

nd

refle

cted

int

o a

phot

odet

ecto

r ce

ll. T

he p

hoto

dete

ctor

se

nses

th

e ch

ange

in

re

flect

ance

w

hen

cond

ensa

tion

occu

rs o

n th

e m

irror

. A

the

rmoc

oupl

e at

tach

ed t

o th

e m

irror

the

n re

cord

s th

e te

mpe

ratu

re a

t w

hich

con

dens

a-tio

n oc

curs

. Aqu

aLab

then

sign

als y

ou b

y fla

shin

g a

gree

n LE

D a

nd/o

r bee

ping

. The

fina

l wat

er a

ctiv

ity a

nd te

mpe

r -at

ure

of th

e sa

mpl

e is

then

disp

layed

. In

add

ition

to

the

tech

niqu

e de

scrib

ed a

bove

, Aqu

aLab

us

es a

n in

tern

al fa

n th

at c

ircul

ates

the

air w

ithin

the

sam

-pl

e ch

ambe

r to

red

uce

equi

libriu

m ti

me.

Sinc

e bo

th d

ew-

poin

t and

sam

ple

surf

ace

tem

pera

ture

s ar

e sim

ulta

neou

sly

mea

sure

d, t

he n

eed

for

com

plet

e th

erm

al eq

uilib

rium

is

elim

inat

ed, w

hich

redu

ces m

easu

rem

ent t

imes

to le

ss th

an

five

min

utes

.

Aq

uaLa

b a

nd T

emp

era

ture

The

Aqu

aLab

Ser

ies 3

doe

s not

con

trol t

empe

ratu

re, m

ak-

ing

it id

eal f

or th

e m

easu

rem

ent o

f sam

ples

at r

oom

tem

-pe

ratu

re.

How

ever

, sa

mpl

es

that

ar

e no

t at

ro

om

tem

pera

ture

dur

ing

the

read

cyc

le w

ill e

quili

brat

e to

the

te

mpe

ratu

re o

f A

quaL

ab b

efor

e th

e w

ater

act

ivity

is d

is-pl

ayed

. La

rge

tem

pera

ture

diff

eren

ces

will

cau

se l

onge

r re

adin

g tim

es, s

ince

a c

ompl

ete

and

accu

rate

rea

ding

will

no

t be

mad

e un

til t

he s

ampl

e an

d th

e in

stru

men

t ar

e w

ithin

2 d

egre

es o

f eac

h ot

her.

To b

ette

r help

you

con

trol

AquaLab

Appendix B

92

Ap

pend

ix B

Aqualab w

ill measure these standards to ±

0.003aw

Table 2: Temperature C

orrection of Decagon’s

Calibration Standards

Temp.

(°C)

H2 O

0.5mK

Cl

6.0mN

aCl

8.57mLiC

l13.41m

LiCl

15.01.000

0.9840.761

0.4920.238

20.01.000

0.9840.760

0.4960.245

25.01.000

0.9840.760

0.5000.250

30.01.000

0.9840.760

0.5040.255

35.01.000

0.9840.760

0.5080.261

40.01.000

0.9840.760

0.5120.266

AquaLab

2. About A

quaLab

7

the temperature difference betw

een your sample and the

instrument, you can access a sam

ple equilibration screen at the m

ain menu that can show

s the difference in temper-

ature between the sam

ple and chamber block (see chpt. 4).

If temperature control is desired, D

ecagon offers a tem-

perature-controlled model, the A

quaLab 4TE. There are

several advantages in having a temperature-controlled

model. H

ere are a few m

ajor reasons:

1.R

esearch p

urp

oses. To study the effects of tempera-

ture on the water activity of a sam

ple, comparison of

the water activity of different sam

ples independent of tem

perature, accelerated shelf-life studies or other w

ater activity studies where tem

perature control is critical. There are m

any shelf-life, packaging, and iso-therm

studies in which the added feature of tem

pera-ture control would be very beneficial.

2.T

o comp

ly with

governm

ent or in

ternal regu

la-tion

s for specific products. Though the water activity

of most products varies by less than ±

0.002 per °C, som

e regulations require measurem

ent at a specific tem

perature. The most com

mon specification is 25°C,

though 20°C is sometim

es indicated.

3.T

o min

imize extrem

e amb

ient tem

peratu

re fluc-

tuation

s. If the environment that the A

quaLab oper-ates in has tem

peratures that fluctuate by as much as ±

Aqu

aLab

App

endi

x A

91

stan

dard

err

or fo

r eac

h sa

lt so

lutio

n, n

ot th

e A

quaL

ab’s

accu

racy

in m

easu

ring

the

salt.

Aqu

aLab

m

easu

res a

ll sa

mpl

es w

ith a

n ac

cura

cy o

f ±0.

003a

w .

4.Sa

tura

ted

salt

solu

tions

are

ver

y te

mpe

ratu

re-s

ensit

ive

and

their

valu

es a

re n

ot a

s acc

urat

e as

the

calib

ratio

n st

anda

rds o

ffere

d by

Dec

agon

.

Ada

pted

from

Gre

ensp

an (1

977)

. Rou

nded

to n

eare

st th

ousa

ndth

.

Tab

le 1

: Wa

ter

Act

ivit

y o

f Se

lect

ed S

alt

So

luti

ons

Satu

rate

d So

lutio

na w

at 2

0° C

a w a

t 25°

C

Lith

ium

C

hlor

ide

0.11

3 ±

0.00

30.

113

± 0.

003

Mag

nesi

umC

hlor

ide

0.33

1 ±

0.00

20.

328

± 0.

002

Pota

ssiu

m

Car

bona

te0.

432

± 0.

003

0.43

2 ±

0.00

4

Mag

nesi

um

Nitr

ate

0.54

4 ±

0.00

20.

529

± 0.

002

Sodi

um

Chl

orid

e0.

755

± 0.

001

0.75

3 ±

0.00

1

Pota

ssiu

m

Chl

orid

e0.

851

± 0.

003

0.84

3 ±

0.00

3

Pota

ssiu

m

Sulfa

te0.

976

± 0.

005

0.97

3 ±

0.00

5

Aqu

aLab

2. A

bout

Aqu

aLab

8

5°C

daily

, wat

er a

ctiv

ity re

adin

gs w

ill v

ary

by ±

0.0

1aw.

Such

var

iatio

ns in

am

bien

t te

mpe

ratu

res

are

unco

m-

mon

. As s

tate

d ab

ove,

this

muc

h un

certa

inty

in sa

mpl

e w

ater

activ

ity is

som

etim

es ac

cept

able,

so th

ere

may

be

no n

eed

for t

empe

ratu

re c

ontro

l. H

owev

er, i

f you

r lab

te

mpe

ratu

re v

aries

to th

is de

gree

and

you

requ

ire b

et-

ter

than

0.0

1aw p

recis

ion,

you

may

wan

t a

tem

pera

-tu

re-c

ontro

lled

mod

el.

If y

our

appl

icatio

n m

eets

any

of

the

crite

ria li

sted

abo

ve,

you

may

wan

t to

use

the

Aqu

aLab

4TE

.

Lim

ita

tio

nsA

quaL

ab’s

only

majo

r lim

itatio

n is

its a

bilit

y to

acc

urat

ely

mea

sure

sam

ples

with

hig

h co

ncen

tratio

ns o

f cer

tain

vol

a-til

es s

uch

as e

than

ol o

r pr

opyle

ne g

lycol

, whi

ch c

an c

o-co

nden

se o

n th

e su

rfac

e of

the

chill

ed m

irror

. Not

all

vol-

atile

s re

act t

his

way

, but

it is

impo

rtant

to n

ote

that

som

e vo

latile

s ca

n af

fect

the

per

form

ance

of

your

inst

rum

ent.

The e

xten

t of t

he ef

fect

is b

oth

conc

entra

tion-

and

mat

rix-

depe

nden

t; th

us,

just

bec

ause

a p

rodu

ct c

onta

ins

som

e et

hano

l or p

ropl

ylene

glyc

ol d

oes n

ot n

eces

saril

y m

ean

the

read

ings

will

be

erro

neou

s. Th

eref

ore,

if yo

ur sa

mpl

e co

n-ta

ins

prop

ylene

glyc

ol o

r a

high

con

cent

ratio

n of

oth

er

volat

iles,

it is

still

pos

sible

to m

ake a

ccur

ate

read

ings

. Ref

er

to t

he s

ectio

n tit

led “

Volat

ile S

ampl

es”

in C

hapt

er 8

or

cont

act D

ecag

on fo

r mor

e de

tails

.

AquaLab

Appendix A

90

Ap

pend

ix A

Prepa

ring Sa

lt Solutio

nIf you choose to m

ix a saturated salt solution for use as a calibration standard, w

e recomm

end that you use the approved AO

AC method. This m

ethod is as follows:

1.Select a reagent-grade salt and place it in a test con-tainer to a depth of about 4cm

for more soluble salts

(lower w

ater activity), to a depth of about 1.5 cm for

less soluble salts (high water activity), and to an inter-

mediate depth for interm

ediate salts.

2.A

dd distilled water in increm

ents of about 2mL, stir-

ring constantly.

3.A

dd water until the salt can absorb no m

ore water,

evidenced by the presence of free liquid. Keep the

amount of free liquid to the m

inimum

needed to keep the solution saturated w

ith water. If you plan on using

this solution over a long term period, seal the solution

well to prevent losses from

evaporation. Below is a

table of saturated salt solutions and their respective w

ater activities at various temperatures. Please note

that these values are based on averaged published data, and the standard errors show

n reflect Greenspan’s

AquaLab

3. Water A

ctivity Theory

9

3. Water A

ctivity Theory

Water is a m

ajor component of foods, pharm

aceuticals, and cosm

etics. Water influences the texture, appearance,

taste and spoilage of these products. There are two basic types of w

ater analysis: water content and w

ater activity.

Mo

isture content

The meaning of the term

moisture content is fam

iliar to m

ost people. It implies a quantitative analysis to determ

ine the total am

ount of water present in a sam

ple. Primary

methods for determ

ining moisture content are loss on

drying and Karlf Fisher titration, but secondary m

ethods such as infrared and N

MR are also used. M

oisture content determ

ination is essential in meeting product nutritional

labeling regulations, specifying recipes and monitoring

processes. How

ever, moisture content alone is not a

reliable indicator for predicting microbial responses and

chemical

reactions in

materials.

The lim

itations of

moisture

content m

easurement

are attributed

to differences in the intensity w

ith which w

ater associates w

ith other components.

Wa

ter activ

ityW

ater activity is a measure of the energy status of the

Aqu

aLab

13. F

urth

er Re

adin

g

89

sens

chaf

t und

-Tec

hnol

ogie.

18:

111-

117.

Lom

auro

, C.J.

, A.S

. Bak

shi,

and

T.P.

Lab

uza.

(198

5). E

val-

uatio

n of

food

moi

stur

e so

rptio

n iso

ther

m e

quat

ions

. Par

t II

: M

ilk,

coffe

e, te

a, nu

ts, o

ilsee

ds,

spice

s an

d st

arch

y fo

ods.

Lebe

nsm

ittel-

Wiss

ensc

haft

und-

Tech

nolo

gie.

18:1

18-1

24.

Yasu

da, H

., H

.G. O

lf, B

. Cris

t, C.

E. L

amaz

e, an

d A

. Pet

er-

lin. (

1972

). M

ovem

ent

of w

ater

in

hom

ogen

eous

wat

er-

swol

len p

olym

ers.

In: W

ater

Str

uctu

re a

t the

Wat

er P

oly-

mer

Int

erfa

ce. J

ellin

ek, H

.H.G

. (ed

.) Pl

enum

Pre

ss, N

ew

York

/Lon

don.

Aqu

aLab

3. W

ater

Act

ivity

The

ory

10

wat

er in

a sy

stem

, and

thus

is a

far b

ette

r ind

icato

r of p

er-

ishab

ility

than

wat

er c

onte

nt. F

igure

1 sh

ows h

ow th

e re

la-tiv

e ac

tivity

of m

icroo

rgan

isms,

lipid

s an

d en

zym

es r

elate

to

wat

er a

ctiv

ity.

Whi

le ot

her

fact

ors,

such

as

nutri

ent

avail

abili

ty a

nd t

empe

ratu

re, c

an a

ffect

the

rela

tions

hips

, w

ater

act

ivity

is

the

best

sin

gle

mea

sure

of

how

wat

er

affe

cts t

hese

pro

cess

es.

Fig.

1: W

ater

Acti

vity D

iagra

m—ad

apted

from

Lab

uza

Wat

er a

ctiv

ity o

f a sy

stem

is m

easu

red

by e

quili

brat

ing

the

liqui

d ph

ase

wat

er i

n th

e sa

mpl

e w

ith t

he v

apor

pha

se

wat

er in

the

head

spac

e an

d m

easu

ring

the

relat

ive

hum

id-

ity o

f the

hea

dspa

ce. I

n th

e A

quaL

ab, a

sam

ple

is pl

aced

in

a sa

mpl

e cu

p w

hich

is se

aled

again

st a

sens

or b

lock

. Ins

ide

the

sens

or b

lock

is a

fan

, a d

ew p

oint

sen

sor,

a te

mpe

ra-

ture

sen

sor,

and

an in

frar

ed th

erm

omet

er. T

he d

ew p

oint

se

nsor

mea

sure

s the

dew

poi

nt te

mpe

ratu

re o

f the

air,

and

AquaLab

13. Further Reading

88

Miscella

neous

Bell, L.N. and T.P. Labuza. (1992). Com

positional influ-ence on the pH

of reduced-moisture solutions. Journal of

Food Science. 57:732-734.

Bell, L.N. and T.P. Labuza. (1994). Influence of the low

-m

oisture state on pH and its im

plication for reaction kinetics. Journal of Food E

ngineering. 22:291-312.

Bell, L.N. (1995). K

inetics of non-enzymatic brow

ning in am

orphous solid systems: D

istinguishing the effects of w

ater activity and the glass transition. Food Research International. 28:591-597.

Brake, N.C. and O

.R. Fennema. (1993). E

dible coatings to inhibit lipid m

igration in a confectionery product. Journal of Food Science. 58:1422-1425.

Dole, M

. and L. Faller. (1950). Water sorption by synthetic

high polymers. Journal of the A

merican Chem

ical Society. 12:414-419.

Fernandez-Salguero J., R. Góm

ez, and M.A

. Carmona.

(1993). Water activity in selected high-m

oisture foods. Journal of Food Com

position and Analysis. 6:364-369.

Lomauro, C.J., A

.S. Bakshi, and T.P. Labuza. (1985). Eval-

uation of food moisture sorption isotherm

equations. Part I: Fruit, vegetable and m

eat products. Lebensmittel-W

is-

AquaLab

3. Water A

ctivity Theory

11

the infrared thermom

eter measures the sam

ple tempera-

ture. From these m

easurements the relative hum

idity of the headspace is com

puted as the ratio of dew point tem

-perature saturation vapor pressure to saturation vapor pressure at the sam

ple temperature. W

hen the water activ-

ity of the sample and the relative hum

idity of the air are in equilibrium

, the measurem

ent of the headspace humidity

gives the water activity of the sam

ple. The purpose of the fan is to speed equilibrium

and to control the boundary layer conductance of the dew

point sensor.

In addition to equilibrium betw

een the liquid phase water

in the sample and the vapor phase, the internal equilib-

rium of the sam

ple is important. If a system

is not at inter-nal

equilibrium,

one m

ight m

easure a

steady vapor

pressure (over the period of measurem

ent) which is not

the true water activity of the system

. An exam

ple of this m

ight be a baked good or a multi-com

ponent food. Ini-tially out of the oven, a baked good is not at internal equi-librium

; the outer surface is at a lower w

ater activity than the center of the baked good. O

ne must w

ait a period of tim

e in order for the water to m

igrate and the system to

come to internal equilibrium

. It is important to rem

ember

the restriction of the definition of water activity to equilibrium.

Temperature Effects

Temperature plays a critical role in w

ater activity determi-

nations. Most critical is the m

easurement of the difference

between sam

ple and dew point tem

perature. If this tem-

Aqu

aLab

13. F

urth

er Re

adin

g

87

Eni

gl, D

.C. a

nd K

.M. S

orre

ls. (1

997)

. Wat

er A

ctiv

ity a

nd

Self-

Pres

ervi

ng F

orm

ulas

. In

: Pre

serv

ativ

e-Fr

ee a

nd S

elf-

Pres

ervi

ng C

osm

etics

and

Dru

gs: P

rincip

les a

nd P

ract

ice.

Kab

ara,

J.J. a

nd D

.S. O

rth (e

d.) M

arce

l Dek

ker,

pp.

45-

73.

Hag

eman

, M.J.

(198

8). T

he ro

le of

moi

stur

e in

pro

tein

sta-

bilit

y. D

rug

Dev

elop

men

t an

d In

dust

rial

Phar

mac

y. 14

(14)

:204

7-20

70.

Heid

eman

n, D

.R. a

nd P

.J. J

aros

z. (1

991)

. Per

form

ulat

ion

stud

ies in

volv

ing

moi

stur

e up

take

in s

olid

dos

age

form

s. Ph

arm

aceu

tical

Rese

arch

. 8(3

):292

-297

.

Fried

el, R

.R. a

nd A

.M. C

unde

ll. (1

998)

. The

app

licat

ion

of

wat

er

activ

ity

mea

sure

men

t to

th

e m

icrob

iolo

gica

l at

tribu

tes

test

ing

of

nons

teril

e ov

er-th

e-co

unte

r dr

ug

prod

ucts.

Pha

rmac

opeia

l For

um. 2

4(2)

:608

7-60

90.

Kon

tny,

M.J.

(19

88).

Dist

ribut

ion

of w

ater

in s

olid

pha

r-m

aceu

tical

syst

ems.

Dru

g D

evelo

pmen

t an

d In

dust

rial

Phar

mac

y. 14

(14)

:199

1-20

27.

Zog

rafi,

G. (

1988

). St

ates

of w

ater

ass

ociat

ed w

ith s

olid

s. D

rug

Dev

elopm

ent a

nd In

dust

rial P

harm

acy.

14(1

4):1

905-

1926

.

Zog

rafi,

G. a

nd M

.J. K

ontn

y. (1

986)

. The

inte

ract

ions

of

wat

er w

ith c

ellul

ose-

and

sta

rch-

deriv

ed p

harm

aceu

tical

excip

ients.

Pha

rmac

eutic

al Re

sear

ch. 3

(4):1

87-1

93.

Aqu

aLab

3. W

ater

Act

ivity

The

ory

12

pera

ture

diff

eren

ce w

ere

in e

rror

by

1°C,

an

erro

r of u

p to

0.

06a w

cou

ld r

esul

t. In

ord

er f

or w

ater

act

ivity

mea

sure

-m

ents

to

be a

ccur

ate

to 0

.001

, te

mpe

ratu

re d

iffer

ence

m

easu

rem

ents

nee

d to

be

accu

rate

to 0

.017

°C. A

quaL

ab’s

infr

ared

ther

mom

eter

mea

sure

s the

diff

eren

ce in

tem

pera

-tu

re b

etw

een

the

sam

ple

and

the

bloc

k. It

is c

aref

ully

cali-

brat

ed t

o m

inim

ize

tem

pera

ture

err

ors,

but

achi

evin

g 0.

017°

C ac

cura

cy is

diff

icult

whe

n te

mpe

ratu

re d

iffer

ence

s ar

e lar

ge.

Best

acc

urac

y is

ther

efor

e ob

tain

ed w

hen

the

sam

ple

is ne

ar c

ham

ber t

empe

ratu

re.

Ano

ther

effe

ct o

f te

mpe

ratu

re o

n w

ater

act

ivity

occ

urs

with

sam

ples

are

nea

r sat

urat

ion.

A sa

mpl

e th

at is

clo

se to

1.

0aw a

nd is

onl

y sli

ghtly

war

mer

tha

n th

e se

nsor

blo

ck

will

con

dens

e w

ater

with

in t

he b

lock

. Th

is w

ill c

ause

er

rors

in t

he m

easu

rem

ent,

and

in s

ubse

quen

t m

easu

re-

men

ts u

ntil

the

cond

ensa

tion

disa

ppea

rs.

A s

ampl

e at

0.

75a w

nee

ds to

be

appr

oxim

ately

4°C

abo

ve th

e ch

ambe

r te

mpe

ratu

re t

o ca

use

cond

ensa

tion.

The

Aqu

aLab

war

ns

the

user

if a

sam

ple

is m

ore

than

4°C

abo

ve th

e ch

ambe

r te

mpe

ratu

re, b

ut fo

r hig

h w

ater

activ

ity sa

mpl

es th

e op

era -

tor

need

s to

be

awar

e th

at c

onde

nsat

ion

can

occu

r if

a sa

mpl

e th

at i

s w

arm

er t

han

the

bloc

k is

put

in t

he

Aqu

aLab

.

Wa

ter

Pote

ntia

lSo

me

addi

tiona

l in

form

atio

n m

ay b

e us

eful

for

und

er-

stan

ding

wha

t wat

er a

ctiv

ity is

and

why

it is

suc

h a

usef

ul

mea

sure

of

moi

stur

e st

atus

in p

rodu

cts.

Wat

er a

ctiv

ity is

AquaLab

13. Further Reading

86

Kusum

egi, K., T. Takahashi, and M

. Miyagi. (1996).

Effects of addition of sodium

citrate on the pasteurizing conditions in “Tuyu”, Japanese noodle soup. Journal of the Japanese Society for Food Science and Technology. 43:740-747.

Sa, M.M

. and A.M

. Sereno. (1993). Effect of tem

perature on sorption isotherm

s and heats of sorption of quince jam

. International Journal of Food Science and Technol-ogy. 28:241-248.

Pharm

aceutica

ls/Co

smetics

Ahlneck, C. and G

. Zografi. (1990). The m

olecular basis of m

oisture effects on the physical and chemical stability

of drugs in the solid state. International Journal of Phar-m

aceutics. 62:87-95.

Cochet, N. and A

.L. Dem

ain. (1996). Effect of w

ater activity on production of beta-lactam

antibiotics by Strep-tom

yces clavuligerus in submerged culture. Journal of

Applied Bacteriology. 80:333-337.

Costantino, H.R., R. Langer, and A

.M. K

libanov. (1994). Solid-phase aggregation of proteins under pharm

aceuti-cally relevant conditions. Journal of Pharm

aceutical Sci-ences. 83:1662-1669.

AquaLab

3. Water A

ctivity Theory

13

closely related to a thermodynam

ic property called the wa-

ter potential, or chemical potential (m

) of water, w

hich is the change in G

ibbs free energy (G) hen w

ater concentra-tion changes. E

quilibrium occurs in a system

when m

is the sam

e everywhere in the system

. Equilibrium

between the

liquid and the vapor phases implies that m

is the same in

both phases. It is this fact that allows us to m

easure the wa -

ter potential of the vapor phase and use that to determine

the water potential of the liquid phase. G

radients in m are

driving forces for moisture m

ovement. Thus, in an isother-

mal system

, water tends to m

ove from regions of high w

a-ter potential (high w

ater activity) to regions of low w

ater potential (low

water activity). W

ater content is not a driving force for w

ater movem

ent, and therefore can not be used to predict the direction of w

ater movem

ent, except in ho-m

ogeneous materials.

Factors in Determining W

ater PotentialThe w

ater potential of the water in a system

is influenced by factors that effect the binding of w

ater. They include osm

otic, matric, and pressure effects. Typically w

ater activ -ity is m

easured at atmospheric pressure, so only the

osmotic and m

atric effects are important.

Osm

otic EffectsO

smotic effects are w

ell known from

biology and physical chem

istry. Water is diluted w

hen a solute is added. If this diluted w

ater is separated from pure w

ater by a semi-per -

Aqu

aLab

13. F

urth

er Re

adin

g

85

lar c

runc

hy c

erea

l fo

ods

at v

ario

us w

ater

act

ivity

lev

els.

Jour

nal o

f the

Scie

nce o

f Foo

d an

d A

gricu

lture

. 70:

347-

354.

Wee

gels,

P.L

., J.A

. Ve

rhoe

k, A

.M.G

. de

Gro

ot,

and

R.J.

Ham

er. (

1994

). E

ffect

s of

glu

ten

of h

eatin

g at

diff

eren

t m

oist

ure

cont

ents

: I.

Chan

ges

in f

unct

iona

l pr

oper

ties.

Jour

nal o

f Cer

eal S

cienc

e. 19

:31-

38.

Bev

era

ges

/So

ups/

Sauc

es/P

rese

rves

Cars

on, K

.J., J

.L. C

ollin

s, an

d M

.P. P

enfie

ld. (

1994

). U

nre-

fined

, drie

d ap

ple

pom

ace

as a

pot

entia

l foo

d in

gred

ient.

Jour

nal o

f Foo

d Sc

ience

. 59:

1213

-121

5.

Dur

rani

, M.J.

, R. K

han,

M. S

aeed

, and

A. K

han.

(19

92).

Dev

elop

men

t of

co

ncen

trate

d be

vera

ges

from

A

nna

appl

es w

ith o

r with

out a

dded

pre

serv

ativ

es b

y co

ntro

lling

ac

tivity

of w

ater

for s

helf

stab

ility.

Sar

had

Jour

nal o

f Agr

i -cu

lture

. 8:2

3-28

.

Ferr

agut

, V.,

J.A. S

alaza

r, an

d A

. Chi

ralt.

(199

3). S

tabi

lity

in

the

cons

erva

tion

of e

mul

sified

sau

ces

low

in o

il co

nten

t. A

limen

taria

. 30:

67-6

9.

Ibar

z, A

., J.

Paga

n, an

d R.

Mig

uelsa

nz. (

1992

). Rh

eolo

gy o

f cla

rified

fru

it ju

ices:

II.

Blac

kcur

rant

jui

ces.

Jour

nal

of

Food

Eng

inee

ring.

15:6

3-74

.

Aqu

aLab

3. W

ater

Act

ivity

The

ory

14

mea

ble

mem

bran

e, w

ater

ten

ds t

o m

ove

from

the

pur

e w

ater

sid

e th

roug

h th

e m

embr

ane

to t

he s

ide

with

the

ad

ded

solu

te. I

f suf

ficien

t pre

ssur

e is

appl

ied to

the

solu

te-

wat

er m

ixtu

re to

just

stop

the

flow,

this

pres

sure

is a

mea

-su

re o

f the

osm

otic

pote

ntial

of t

he s

olut

ion.

Add

ition

of

one

mol

e of

an

idea

l sol

ute

to a

kilo

gram

of

wat

er p

ro-

duce

s an

osm

otic

pres

sure

of

22.4

atm

. Thi

s lo

wer

s th

e w

ater

act

ivity

of

the

solu

tion

from

1.0

to

0.98

a w. F

or a

gi

ven

amou

nt o

f so

lute

, inc

reas

ing

the

wat

er c

onte

nt o

f th

e sy

stem

s di

lute

s th

e so

lute

, de

crea

sing

the

osm

otic

pr

essu

re, a

nd in

crea

sing

the

wat

er a

ctiv

ity. S

ince

micr

obial

ce

lls a

re h

igh

conc

entra

tions

of

solu

te s

urro

unde

d by

se

mi-p

erm

eabl

e m

embr

anes

, th

e os

mot

ic ef

fect

on

the

free

ene

rgy

of t

he w

ater

is

impo

rtan

t fo

r de

term

inin

g m

icrob

ial w

ater

relat

ions

and

ther

efor

e th

eir a

ctiv

ity.

Mat

ric

Effe

cts

The

sam

ple

mat

rix a

ffect

s w

ater

act

ivity

by

phys

ically

bi

ndin

g w

ater

with

in it

s st

ruct

ure

thro

ugh

adhe

sive

and

cohe

sive

forc

es t

hat

hold

wat

er in

por

es a

nd c

apill

aries

, an

d to

par

ticle

surf

aces

. If c

ellul

ose

or p

rote

in w

ere

adde

d to

wat

er, t

he e

nerg

y st

atus

of t

he w

ater

wou

ld b

e re

duce

d.

Wor

k wo

uld

need

to

be d

one

to e

xtra

ct t

he w

ater

fro

m

this

mat

rix. T

his r

educ

tion

in e

nerg

y st

atus

of t

he w

ater

is

not

osm

otic,

bec

ause

the

cell

ulos

e or

pro

tein

con

cent

ra-

tions

are

far t

oo lo

w to

pro

duce

any

sign

ifica

nt d

ilutio

n of

w

ater

. The

redu

ctio

n in

ene

rgy

is th

e re

sult

of d

irect

phy

s-ica

l bin

ding

of w

ater

to th

e ce

llulo

se o

r pro

tein

mat

rix b

y hy

drog

en b

ondi

ng a

nd v

an d

er W

aal

forc

es.

At

high

er

AquaLab

13. Further Reading

84

Harris, M

. and M. Peleg. (1996). Patterns of textural

changes in brittle cellular cereal foods caused by moisture

sorption. Cereal Chemistry. 73:225-231.

Michniew

icz, J., C.G. Biliaderis, and W

. Bushuk. (1992). E

ffect of added pentosans on some properties of w

heat bread. Food Chem

istry. 43:251-257.

Ramanathan, S. and S. Cenkow

ski. (1995). Sorption iso-therm

s of flour and flow behaviour of dough as influ-

enced by

flour com

paction. Canadian

Agricultural

Engineering. 37:119-124.

Roessler, P.F. and M.C. Ballenger. (1996). Contam

ination of an unpreserved sem

isoft baked cookie with a xerophilic

Aspergillus species. Journal of Food Protection. 59:1055-

1060.

Seiler, D.A

.L. (1979). The mould-free shelf life of bakery

products. FMBRA

Bulletin. April(2):71-74.

Sumner, S.S., J.A

. Albrecht, and D

.L. Peters. (1993). O

ccurrence of enterotoxigenic strains of Staphylococcus aureus and enterotoxin production in bakery products. Journal of Food Protection. 56:722-724.

Tesch, R., M.D

. Norm

and, and M. Peleg. (1996). Com

pari-son of the acoustic and m

echanical signatures of two cellu-

AquaLab

3. Water A

ctivity Theory

15

water activity levels, capillary forces and surface tension

can also play a role.

Sorp

tion Iso

therms

Relating Water A

ctivity to Water C

ontentChanges in w

ater content affect both the osmotic and

matric binding of w

ater in a product. Thus a relationship exists betw

een the water activity and w

ater content of a product. This relationship is called the sorption isotherm

, and is unique for each product. Besides being unique to each

product, the

isotherm

changes depending

on w

hether it was obtained by drying or w

etting the sample.

These factors need to be kept in mind if one tries to use

water content to infer the stability or safety of a product.

Typically, large safety margins are built in to w

ater content specifications to allow

for these uncertainties.

While the sorption isotherm

is often used to infer water

activity from w

ater content, one could easily go the other direction and use the w

ater activity to infer the water con-

tent. This is particularly attractive because water activity is

much m

ore quickly measured than w

ater content. This m

ethod gives particularly good precision in the center of the isotherm

. In order to infer water content from

water

activity, one needs an isotherm for the particular product;

produced, ideally, using the process that brings the prod -uct to its final w

ater content.

Aqu

aLab

13. F

urth

er Re

adin

g

83

Zeb,

A.,

R. K

han,

A.

Kha

n, M

. Sa

eed,

and

S.A

. M

anan

. (1

994)

. Inf

luen

ce o

f cry

stalli

ne s

ucro

se a

nd c

hem

ical p

rese

r-va

tives

on

the w

ater

activ

ity an

d sh

elf st

abili

ty o

f int

erm

ediat

e ba

nana

chip

s. Sa

rhad

Jour

nal o

f Agr

icultu

re. 1

0:72

1-72

6.

Zhan

g, X

.W.,

X. L

iu, D

.X. G

u, W

. Zho

u, R

.L. W

ang,

and

P.

Liu.

(19

96).

Des

orpt

ion

isoth

erm

s of

som

e ve

geta

bles

. Jo

urna

l of t

he S

cienc

e of F

ood

and

Agr

icultu

re. 7

0:30

3-30

6.

Bak

ed G

oo

ds

and

Cer

eals

Ara

mou

ni, F

.M.,

K.K

. Kon

e, J.A

. Cra

ig, a

nd D

.-Y.C

. Fun

g. (1

994)

. G

row

th o

f Cl

ostri

dium

spo

roge

nes

PA 3

679

in

hom

e-st

yle c

anne

d qu

ick b

read

s. Jo

urna

l of F

ood

Prot

ec-

tion.

57:

882-

886.

Caha

gnier

, B.,

L. L

esag

e, an

d M

.D. R

ichar

d. (1

993)

. Mou

ld

grow

th a

nd c

onid

iatio

n in

cer

eal

grain

s as

affe

cted

by

wat

er a

ctiv

ity a

nd te

mpe

ratu

re. L

ette

rs I

n A

pplie

d M

icro -

biol

ogy.

17:7

-13.

Claw

son,

A.R

. and

A.J.

Tay

lor.

(199

3). C

hem

ical c

hang

es

durin

g co

okin

g of

whe

at. F

ood

Chem

istry

. 47:

337-

343.

Góm

ez, R

., Fe

rnan

dez-

Salg

uero

J., M

.A. C

arm

ona,

and

D.

Sanc

hez.

(199

3). W

ater

act

ivity

in fo

ods w

ith in

term

ediat

e m

oist

ure

leve

ls: B

aker

y an

d co

nfec

tione

ry p

rodu

cts:

Mis-

cella

ny. A

limen

taria

. 30:

55-5

7.

Aqu

aLab

3. W

ater

Act

ivity

The

ory

16

For

exam

ple,

if on

e w

ere

usin

g th

e A

quaL

ab to

mon

itor

the

wat

er c

onte

nt o

f drie

d po

tato

flak

es, o

ne w

ould

mea

-su

re th

e w

ater

act

ivity

and

wat

er c

onte

nt o

f pot

ato

flake

s dr

ied

to v

aryin

g de

gree

s usin

g th

e st

anda

rd d

ryin

g pr

oces

s fo

r tho

se fl

akes

. An

isoth

erm

wou

ld b

e co

nstr

ucte

d us

ing

thos

e da

ta, a

nd th

e w

ater

con

tent

wou

ld b

e in

ferr

ed u

sing

the

mea

sure

d w

ater

act

ivity

of s

ampl

es a

nd th

at is

othe

rm.

The

impo

rtanc

e of

the

conc

ept o

f wat

er a

ctiv

ity o

f foo

ds,

phar

mac

eutic

als, a

nd c

osm

etics

can

not b

e ov

erly

emph

a -siz

ed. W

ater

act

ivity

is a

mea

sure

of

the

ener

gy s

tatu

s of

th

e w

ater

in a

syst

em. M

ore

impo

rtan

tly, t

he u

sefu

lnes

s of

wat

er a

ctiv

ity i

n re

latio

n to

micr

obial

gro

wth

, ch

emica

l re

activ

ity,

and

sta

bilit

y ov

er w

ater

con

tent

has

bee

n sh

own.

AquaLab

13. Further Reading

82

Kiranoudis, C.T., Z

.B. Maroulis, E

. Tsami, and K

.D. M

ari-nos. (1993). E

quilibrium m

oisture content and heat of desorption of som

e vegetables. Journal of Food Engineer -

ing. 20:55-74.

Makow

er, B. and G.L. D

ehority. (1943). Equilibrium

mois-

ture content of dehydrated vegetables. Industrial and E

ngineering Chemistry. 35(2):193-197.

Maltini, E

., D. Torreggiani, B.R. Brovetto, and G

. Bertolo. (1993). Functional properties of reduced m

oisture fruits as ingredients in food system

s. Food Research International. 26:413-419.

Marin, S., V. Sanchis, and N

. Magan. (1995). W

ater activity, tem

perature, and pH effects on grow

th of Fusarium

moniliform

e and Fusarium proliferatum

isolates from

maize. Canadian Journal of M

icrobiology. 41:1063-1070.

Monsalve-G

onzalez, A., G

.V. Barbosa-Canovas, and R.P. Cavalieri. (1993). M

ass transfer and textural changes dur -ing processing of apples by com

bined methods. Journal of

Food Science. 58:1118-1124.

Tapia de Daza, M

.S., C.E. A

guilar, V. Roa, and R.V. Diaz

de Tablante. (1995). Combined stress effects on grow

th of Z

ygosaccharomyces rouxii from

an intermediate m

oisture papaya product. Journal of Food Science. 60:356-359.

AquaLab

4. G

etting Started

17

4. G

etting Sta

rted

Co

mp

onents o

f yo

ur Aq

uaLa

bYour A

quaLab should have been shipped with the follow

-ing item

s:

•A

qu

aLab

water activity m

eter

•P

ower cord

•R

S-232 interface cab

le

•100 d

isposab

le samp

le cup

s

•O

perator’s M

anual

•Q

uick Start gu

ide

•C

leanin

g Kit

•3 vials each

of the follow

ing calib

ration solu

tions:

1.000aw Distilled W

ater0.760aw 6.0 m

olal NaCl

0.500aw 8.57 m

olal LiCl0.250aw 13.41 m

olal LiCl

Cho

osing

a Lo

catio

nTo ensure that your A

quaLab operates correctly and con-sistently, place it on a level surface. This reduces the chance that sam

ple material w

ill spill and contaminate the sam

ple cham

ber. Also select a location w

here the temperature

remains fairly stable to avoid tem

perature changes that can affect accuracy. This location should be well away from

air

Aqu

aLab

13. F

urth

er Re

adin

g

81

Viv

ier,

D.,

M. R

ivem

ale, J

.P. R

ever

bel,

R. R

atom

ahen

ina,

and

P. G

alzy.

(199

4). S

tudy

of

the

grow

th o

f ye

asts

fro

m

feta

che

ese.

Inte

rnat

iona

l Jou

rnal

of F

ood

Micr

obio

logy

. 22

:207

-215

.

Viv

ier, D

., R.

Rat

omah

enin

a, an

d P.

Galz

y. (1

994)

. Cha

rac-

teris

tics

of m

icroc

occi

from

the

sur

face

of

Roqu

efor

t ch

eese

. Jou

rnal

of A

pplie

d Ba

cter

iolo

gy. 7

6:54

6-55

2.

Frui

ts a

nd V

eget

ab

les

Ayu

b, M

., R.

Kha

n, S

. Wah

ab, A

. Zeb

, and

J. M

uham

mad

. (1

995)

. Effe

ct o

f cry

stall

ine

swee

tene

rs o

n th

e w

ater

act

iv-

ity a

nd sh

elf st

abili

ty o

f osm

otica

lly d

ehyd

rate

d gu

ava.

Sar-

had

Jour

nal o

f Agr

icultu

re. 1

1:75

5-76

1.

Beve

ridge

, T.

an

d S.

E.

Wein

traub

. (1

995)

. E

ffect

of

bl

anch

ing

pret

reat

men

t on

col

or a

nd t

extu

re o

f ap

ple

slice

s at

var

ious

wat

er a

ctiv

ities

. Foo

d Re

sear

ch I

nter

na-

tiona

l. 28

:83-

86.

Hub

inge

r, M

., F.C

. Men

egall

i, R.

J. A

guer

re, a

nd C

. Sua

rez.

(199

2). W

ater

vap

or a

dsor

ptio

n iso

ther

ms

of g

uava

, man

go

and

pine

appl

e. Jo

urna

l of F

ood

Scien

ce. 5

7:14

05-1

407.

Jimen

ez, M

., M

. Man

ez, a

nd E

. Her

nand

ez. (

1996

). In

flu-

ence

of w

ater

act

ivity

and

tem

pera

ture

on

the

prod

uctio

n of

zea

rale

none

in c

orn

by th

ree

Fusa

rium

spec

ies.

Inte

rna-

tiona

l Jou

rnal

of F

ood

Micr

obio

logy

. 29:

417-

421.

Aqu

aLab

4. G

ettin

g St

arte

d

18

cond

ition

er an

d he

ater

ven

ts, o

pen

win

dow

s, et

c. P

lace

the

Aqu

aLab

in a

loca

tion

whe

re c

leanl

ines

s can

be

main

tain

ed

to p

reve

nt c

onta

min

atio

n of

the s

ampl

e cha

mbe

r.

Fea

ture

s

Fron

t view

of A

quaL

ab

Back

view

of A

quaL

ab

light

LED

indi

cato

rFu

nctio

n Ke

ys

Sam

ple

draw

er

LCD

RS-2

32 in

terfa

ce

fuse

wel

lO

N/O

FF S

witc

h

Pow

er c

ord

Plug

Fan

Lid th

umb-

scre

w

AquaLab

13. Further Reading

80

Da

iry Pro

ducts

Fresno, J.M., M

.E. Tornadijo, J. Carballo, P.J. G

onzalez, and A

. Bernardo. (1996). Characterization and biochemi-

cal changes during the ripening of a Spanish craft goat’s m

ilk cheese (Arm

ada variety). Food Chemistry. 55:225-

230.

Hong, Y.H

. (1991). Physical and chemical properties of

the process cheese on the domestic m

arket. Korean Jour-

nal of Anim

al Science. 33:387-391.

Kom

bila, M.E

. and C. Lacroix. (1991). The effect of com-

binations of salt, lactose and glycerol on the water activity

(aw ) of cheese spreads. Canadian Institute of Food Science and Technology Journal. 24:233-238.

Pisecky, J. (1992). Water activity of m

ilk powders. M

ilch-w

issenschaft. 47:3-7.

Tornadijo, E., J.M

. Fresno, J. Carballo, and S.R. Martin.

(1993). Study of Enterobacteriaceae throughout the m

anu-facturing and ripening of hard goats’ cheese. Journal of A

pplied Bacteriology. 75:240-246.

Valik, L. and F. Gorner. (1995). E

ffect of water activity

adjusted with different solutes on grow

th and Lactic acid production by Lactobacillus helveticus. Folia M

icrobiolog -ica. 40:472-474.

AquaLab

4. G

etting Started

19

Prepa

ring A

qua

Lab

for O

pera

tion

After finding a good location for your A

quaLab, plug the pow

er cord into the back of the unit. Before turning it on, turn the knob to the “O

PEN

/LOA

D” position, pull open

the sample draw

er and remove the em

pty disposable sam-

ple cup. This empty cup is placed in the draw

er to protect it during shipm

ent. Turn the instrument on (see features

diagram). The follow

ing screens will appear on the LCD

.

(Note: the “v.3.0” shown the above illustration is an example show-

ing the version of operating code used in the instrument. We periodi-

cally update the code and add new features, so if your AquaLab

shows a version number higher than this, don’t be alarmed.)

Then the screen will autom

atically shift to the measure-

ment screen show

n below:

This is the measurem

ent screen, displaying the water activ-

ity (aw ) on the top left portion of the screen, and the sam-

ple temperature in the low

er right.

AQUALAB

Series 3B v 3.0

0.000

a0.0 °C

w

Aqu

aLab

13. F

urth

er Re

adin

g

79

Luec

ke,

F.K

. (1

994)

. Fe

rmen

ted

mea

t pr

oduc

ts. F

ood

Rese

arch

Inte

rnat

iona

l. 27

:299

-307

.

Min

egish

i, Y.

, Y. T

suka

mas

a, K

. Miak

e, T.

Shi

mas

aki,

C.

Imai,

M. S

ugiya

ma,

and

H. S

hina

no. (

1995

). W

ater

act

ivity

an

d m

icrof

lora

in

com

mer

cial

vacu

um-p

acke

d sm

oked

sa

lmon

s. Jo

urna

l of

the

Food

Hyg

ienic

Socie

ty o

f Ja

pan.

36

:442

-446

.

Roch

a-G

arza

, A

.E.

and

J.F.

Zay

as.

(199

6).

Qua

lity

of

broi

led b

eef

patti

es s

uppl

emen

ted

with

whe

at g

erm

pro

-te

in fl

our.

Jour

nal o

f Foo

d Sc

ience

. 61:

418-

421.

Shim

asak

i, T.

, K. M

iake,

Y. T

suka

mas

a, M

.A. S

ugiya

ma,

Y.

Min

egish

i, an

d H

. Shi

nano

. (19

94).

Effe

ct o

f Wat

er A

ctiv

ity

and

Stor

age

Tem

pera

ture

on

the

Qua

lity

and

Micr

oflo

ra o

f Sm

oked

Salm

on. N

ippo

n Su

isan

Gak

kaish

i. 60

:569

-576

.

Unt

erm

ann,

F. a

nd C

. Mul

ler. (

1992

). In

fluen

ce o

f aw v

alue

and

stor

age

tem

pera

ture

on

the

mul

tiplic

atio

n an

d en

tero

-to

xin

form

atio

n of

sta

phylo

cocc

i in

dry-

cure

d ra

w h

ams.

Inte

rnat

iona

l Jou

rnal

of F

ood

Micr

obio

logy

. 16:

109-

115.

Will

iams,

S.K

., G

.E.

Rodr

ick,

and

R.L.

Wes

t. (1

995)

. So

dium

lact

ate

affe

cts

shelf

life

and

con

sum

er a

ccep

tanc

e of

fre

sh (

Icta

luru

s ne

bulo

sus,

mar

mor

atus

) fil

lets

unde

r sim

ulat

ed

reta

il co

nditi

ons.

Jour

nal

of

Food

Sc

ience

. 60

:636

-639

.

Aqu

aLab

4. G

ettin

g St

arte

d

20

In o

rder

to

prov

ide

the

mos

t ac

cura

te r

eadi

ngs,

your

A

quaL

ab sh

ould

idea

lly b

e all

owed

to w

arm

-up

for a

t lea

st

15 m

inut

es a

fter

turn

ing

it on

. Thi

s all

ows

the

air in

side

the

Aqu

aLab

to e

quili

brat

e to

the

tem

pera

ture

of

its s

ur-

roun

ding

s.

AquaLab

13. Further Reading

78

Clavero, M.R.S. and L.R. Beuchat. (1996). Survival of

Escherichia coli O

157:H7 in broth and processed salam

i as influenced by pH

, water activity, and tem

perature and suitability of m

edia for its recovery. Applied and E

nviron -m

ental Microbiology. 62:2735-2740.

Duffy, L.L., P.B. Vanderlinde, and F.H

. Grau. (1994).

Grow

th of Listeria monocytogenes on vacuum

-packed cooked m

eats: Effects of pH

, a w, nitrite and ascorbate. International Journal of Food M


Fernandez-Salguero J., R. Góm

ez, and M.A

. Carmona.

(1994). Water activity of Spanish interm

ediate-moisture

meat products. M

eat Science. 38:341-346.

Góm

ez, R. and Fernandez-Salguero J. (1993). Note: W

ater activity of Spanish interm

ediate moisture fish products.

Revista Espanola D

e Ciencia Y Tecnologia D

e Alim

entos. 33:651-656.

Hand, L. (1994). Controlling w

ater activity and pH in

snack sticks. Meat M

arketing and Technology. May:55-56.

Lee, M.B. and S. Styliadis. (1996). A

survey of pH and

water activity levels in processed salam

is and sausages in M

etro Toronto. Journal of Food Protection. 59:1007-1010.

AquaLab

5. The Menus

21

5. The Menus

The Mea

surement Screen

Each tim

e you turn on your AquaLab, the screen above

will appear. A

s mentioned earlier, the w

ater activity and sam

ple temperature are displayed on the screen. O

n each side of the LCD

there are two buttons. Each button per-

forms a different function. Follow

ing is a description of the m

odes and options you may use, and the buttons used

to set them.diagram of button options from main menu

Cha

nging

Lang

uag

esThe A

quaLab comes to you w

ith English as the default

0.000

a0.0 °C

w

temperature equilibration screen

system setup

continuous/normal

0.000

a0.0 °C

w

languageselection

mode

Aqu

aLab

13. F

urth

er Re

adin

g

77

Toku

oka,

K. a

nd T

. Ish

itani

. (19

91).

Min

imum

wat

er a

ctiv

-iti

es f

or t

he g

row

th o

f ye

asts

iso

lated

fro

m h

igh-

suga

r fo

ods.

Jour

nal

of G

ener

al an

d A

pplie

d M

icrob

iolo

gy.

37:1

11-1

19.

Uca

r, F.

and

I. G

uner

i. (1

996)

. The

effe

ct o

f wat

er a

ctiv

ity

(aw),

pH a

nd t

empe

ratu

re o

n th

e gr

owth

of

osm

ophi

lic

yeas

ts. T

urki

sh Jo

urna

l of B

iolo

gy. 2

0:37

-46.

Wijt

zes,

T., P

.J. M

cclu

re, M

.H. Z

wiet

erin

g, a

nd T

.A. R

ob-

erts.

(199

3). M

odell

ing

bact

erial

gro

wth

of L

ister

ia m

ono-

cyto

gene

s as

a

func

tion

of

wat

er

activ

ity,

pH

and

tem

pera

ture

. Int

erna

tiona

l Jou

rnal

of F

ood

Micr

obio

logy

. 18

:139

-149

.

Zw

ieter

ing,

M.H

., T.

Wijt

zes,

J.C. D

e-W

it, a

nd R

.K. V

an’T

. (1

992)

. A d

ecisi

on s

uppo

rt sy

stem

for

pre

dict

ion

of t

he

micr

obial

spo

ilage

in f

oods

. Jou

rnal

of F

ood

Prot

ectio

n.

55:9

73-9

79.

Wa

ter

Act

ivit

y i

n Fo

od

s

Mea

t a

nd S

eafo

od

Chen

, N. a

nd L

.A. S

helef

. (19

92).

Relat

ions

hip

betw

een

wat

er a

ctiv

ity, s

alts

of la

ctic

acid

, and

gro

wth

of

List

eria

mon

ocyt

ogen

es in

a m

eat m

odel

syst

em. J

ourn

al of

Foo

d Pr

otec

tion.

55:

574-

578.

Aqu

aLab

5. T

he M

enus

22

on-s

cree

n us

er la

ngua

ge. I

f you

pre

fer n

ot to

use

Eng

lish,

yo

u ca

n ch

ange

it to

one

of

a va

riety

of

othe

r lan

guag

es:

Ger

man

, Fre

nch,

Spa

nish

, Ita

lian,

Sw

edish

, Dan

ish, N

or-

weg

ian,

Czec

h, P

ortu

gues

e, Ja

pane

se,

Polis

h or

Fin

nish

. Th

is is

done

sim

ply

by p

ress

ing

the

uppe

r rig

ht b

utto

n of

th

e in

stru

men

t w

hile

the

draw

er k

nob

is in

the

OPE

N/

LOA

D p

ositi

on. Y

ou w

ill se

e th

e fo

llow

ing

scre

en:

Pres

s th

e up

per

right

key

aga

in,

and

the

next

lan

guag

e op

tion

(Ger

man

) will

app

ear:

Eac

h tim

e you

pre

ss th

e rig

ht b

utto

n, th

e disp

lay w

ill sc

roll

to t

he n

ext

langu

age

optio

n. S

elec

t th

e de

sired

lang

uage

, th

en p

ress

the

low

er le

ft bu

tton

to e

xit.

No

rma

l Sa

mp

ling

Mo

de

The

first

tim

e yo

u tu

rn o

n th

e A

quaL

ab, i

t will

be

in n

or-

mal

sam

plin

g m

ode.

In th

is m

ode,

the

sam

ple

is m

easu

red

once

, afte

r whi

ch th

e in

stru

men

t not

ifies

you

that

it is

fin-

ished

with

a se

ries o

f fou

r bee

ps an

d a g

reen

flas

hing

ligh

t. Th

e op

erat

or h

as th

e ab

ility

to c

hang

e th

e sa

mpl

ing

mod

e an

d th

e au

dibl

e ala

rm.

English

-exit-

Deutsch

-zurück-

AquaLab

13. Further Reading

76

Petersson, S. and J. Schnuerer. (1995). Biocontrol of mold

growth in high-m

oisture wheat stored under airtight con-

ditions by Pichia anomala, Pichia guillierm

ondii, and Sac-charom

yces cerevisiae.

Applied

and E

nvironmental

Microbiology. 61:1027-1032.

Pitt, J.I. and B.F. Miscam

ble. (1995). Water relations of

Aspergillus flavus and closely related species. Journal of

Food Protection. 58:86-90.

Quintavalla, S. and G

. Parolari. (1993). Effects of tem

pera-ture, aw and pH

on the growth of Bacillus cells and spore:

A

response surface

methodology

study. International

Journal of Food Microbiology. 19:207-216.

Saad, R.R. (1992). Effect of water activity on growth and lip-ids of xerophilic fungi, A

spergillus repens and Aspergillus

amstelodam

i. Zentralblatt Fuer Mikrobiologie. 147:61-64.

Santos, J., T.M. Lopez-D

iaz, M.L. G

arcia-Lopez, M.C.

Garcia-Fernandez, and A

. Otero. (1994). M

inimum

water

activity for the growth of A

eromonas hydrophila as

affected by strain, temperature and hum

ectant. Letters In A

pplied Microbiology. 19:76-78.

Tapia de Daza, M

.S., Y. Villegas, and A

. Martinez. (1991).

Minim

al water activity for grow

th of Listeria monocytoge -

nes as affected by solute and temperature. International

Journal of Food Microbiology. 14:333-338.

AquaLab

5. The Menus

23

Co

ntinuous M

od

eContinuous m

ode reads your sample continuously until

you turn the knob to the OPE

N/LO

AD

position. It will

read the sample, display the w

ater activity and sample tem

-perature, then begin another read cycle w

ithout turning the knob. Betw

een samples, it w

ill signal you with the

green LED

flash, accompanied by the beeper (if it is

enabled).

To toggle between the norm

al and continuous modes,

press the top left button. The display will show

a small “c”

to the left of the water activity readings:

main menu with continuous mode enabled

If you press the upper left button again, the “c” will disap-

pear and you will be back in norm

al sampling m

ode.

Temp

erature Eq

uilibra

tion Screen

To see the temperature difference betw

een your sample

and the AquaLab, press the low

er right button at the main

menu. This screen can only be accessed w

hen the drawer

0.000

a0.0 °C

w

c

“c” for continuous mode

Aqu

aLab

13. F

urth

er Re

adin

g

75

Kun

tz, L

.A. (

1992

). K

eepi

ng m

icroo

rgan

isms

in c

ontro

l. Fo

od P

rodu

ct D

esig

n. A

ugus

t:44-

51.

Li, K

.Y. a

nd J.

A. T

orre

s. (1

993)

. Wat

er a

ctiv

ity re

latio

nshi

ps

for s

elect

ed m

esop

hiles

and

psy

chro

troph

s at

refri

gera

tion

tem

pera

ture

. Jou

rnal

of F

ood

Prot

ectio

n. 5

6:61

2-61

5.

Mar

ausk

a, M

., A

. V

igan

ts, A

. K

linca

re,

D.

Upi

te,

E.

Kam

insk

a, an

d M

. Be

kers

. (1

996)

. In

fluen

ce o

f w

ater

ac

tivity

and

med

ium

osm

olali

ty o

n th

e gr

owth

and

aci

d pr

oduc

tion

of L

acto

bacil

lus

case

i var

. alac

tosu

s. Pr

ocee

d -in

gs o

f the

Lat

vian

Aca

dem

y of

Scie

nces

Sec

tion

B N

atu-

ral E

xact

and

App

lied

Scie

nces

. 50:

144-

146.

Mill

er,

A.J.

(19

92).

Com

bine

d w

ater

act

ivity

and

sol

ute

effe

cts

on g

row

th a

nd s

urvi

val o

f List

eria

mon

ocyt

ogen

es

Scot

t A. J

ourn

al of

Foo

d Pr

otec

tion.

55:

414-

418.

Nak

ajo, M

. and

Y. M

oriy

ama.

(199

3). E

ffect

of

pH a

nd

wat

er ac

tivity

on

heat

resis

tanc

e of s

pore

s of B

acill

us co

ag-

ulan

s. Jo

urna

l of

the

Japa

nese

Soc

iety

for

Food

Scie

nce

and

Tech

nolo

gy. 4

0:26

8-27

1.

Nol

an, D

.A.,

D.C

. Cha

mbl

in, a

nd J.

A. T

rolle

r. (1

992)

. Min

-im

al w

ater

act

ivity

leve

ls fo

r gro

wth

and

sur

viva

l of L

iste-

ria m

onoc

ytog

enes

and

List

eria

inno

cua.

Inte

rnat

iona

l Jo

urna

l of F

ood

Micr

obio

logy

. 16:

323-

335.

Aqu

aLab

5. T

he M

enus

24

knob

is

in t

he O

PEN

/LO

AD

pos

ition

. Th

e fo

llow

ing

scre

en w

ill a

ppea

r:

This

scre

en sh

ows t

he te

mpe

ratu

re d

iffer

ence

bet

wee

n th

e sa

mpl

e (T

s) a

nd th

e ch

ambe

r bl

ock

(Tb)

, allo

win

g yo

u to

qu

ickly

chec

k if

the

sam

ple

is to

o ho

t, w

hich

may

cau

se

cond

ensa

tion

insid

e th

e ch

ambe

r. Pr

ess

the

low

er r

ight

bu

tton

to e

xit.

Syst

em C

onf

igur

ati

on

If y

ou p

ress

the

botto

m le

ft bu

tton

whi

le at

the

mea

sure

-m

ent s

cree

n, it

will

brin

g yo

u to

the

syst

em c

onfig

urat

ion

men

u.

This

men

u all

ows

you

to m

ake

min

or s

yste

m c

hang

es.

From

this

men

u, y

ou c

an c

hang

e th

e au

dibl

e ala

rm a

fter

each

sam

ple

or e

nter

the

linea

r offs

et a

djus

tmen

t men

u.

Ts - Tb = 0.125

Ts = 23.1

syst

em c

onfig

urat

ion

men

u bu

tton

0.000

a0.0 °C

w

AquaLab

13. Further Reading

74

Garcia de Fernando, G.D., O. D

iaz, M. Fernandez, and J.A.

Ordonez. (1992). Changes in water activity of selected solid cul-

ture media throughout incubation. Food M


Gibson, A

.M., J. Baranyi, J.I. Pitt, M

.J. Eyles, and T.A

. Roberts. (1994). Predicting fungal grow

th: The effect of w

ater activity on Aspergillus flavus and related species.

International Journal of Food Microbiology. 23:419-431.

Goaleni, N

., J.E. Sm

ith, J. Lacey, and G. G

ettinby. (1997). E

ffects of temperature, w

ater activity, and incubation time

on production of aflatoxins and cyclopiazonic acid by an isolate

of A

spergillus flavus

in surface

agar culture.

Applied and E

nvironmental M


Hocking, A

.D. and B.F. M

iscamble. (1995). W

ater relations of som

e Zygom

ycetes isolated from food. M

ycological Research. 99:1113-1118.

Hocking, A

.D., B.F. M

iscamble, and J.I. Pitt. (1994). W

ater relations of A

lternaria alternata, Cladosporium cladosporio-

ides, Cladosporium sphaerosperm

um, Curvularia lunata

and Curvularia pallescens. Mycological Research. 98:91-94.

Houtsm

a, P.C., A. H

euvelink, J. Dufrenne, and S. N

oter-m

ans. (1994). Effect of sodium

lactate on toxin produc-tion, spore germ

ination and heat resistance of proteolytic Clostridium

botulinum strains. Journal of Food Protec-

tion. 57:327-330.

AquaLab

5. The Menus

25

System configuration menu

Com

pletion Notification

When you are sam

pling, the AquaLab has two w

ays of notifying you that the w

ater activity reading is complete:

an audible alarm and a flashing green LE

D, located on the

left front corner of the AquaLab’s case. In norm

al sam-

pling mode, w

hen a sample is started, the LE

D w

ill flash once, and w

hen it is finished it will flash continuously until

the knob is moved to the O

PEN

/LOA

D position (if not

operating in continuous mode). You cannot turn off or

change the LED

flashing functions.

There are three audible alarm options, represented by

three icons as shown below.

definition of beeper icons

BeeperBeeperM

ode indicatorLinear offset

menu

Icon(continuous show

n)

0x

4x

No beeping.

Beeps four times, then stops.

Beeps until drawer is opened.

Aqu

aLab

13. F

urth

er Re

adin

g

73

food

pol

ymer

scie

nce:

Impl

icatio

ns o

f st

ate

on a

rrhe

nius

an

d W

LF m

odels

in p

redi

ctin

g sh

elf li

fe. J

ourn

al of

Foo

d E

ngin

eerin

g. 22

:271

-289

.

Rock

land,

L.B

. and

G.F

. Ste

war

t. (1

981)

. Wat

er A

ctiv

ity:

Influ

ence

s on

Food

Qua

lity.

Aca

dem

ic Pr

ess,

New

Yor

k.

Rock

land,

L.B

. and

S.K

. Nish

i. (1

980)

. Inf

luen

ce o

f wat

er

activ

ity o

n fo

od p

rodu

ct q

ualit

y an

d st

abili

ty. F

ood

Tech

-no

logy

. 34:

42-5

9.

Seow

, C.C

., T.

T. T

eng,

and

C.H

. Qua

h. (1

988)

. Foo

d Pr

es-

erva

tion

by M

oist

ure

Cont

rol.

Else

vier

, New

Yor

k.

Taou

kis,

P., W

. Bre

ene,

and

T.P.

Lab

uza.

(198

8). I

nter

med

i-at

e m

oist

ure

food

s. A

dvan

ces i

n Ce

real

Scien

ce a

nd T

ech-

nolo

gy. 9

:91-

128.

Wa

ter

Act

ivit

y a

nd M

icro

bio

log

yBe

ucha

t, L.

R. (

1981

). M

icrob

ial s

tabi

lity

as a

ffect

ed b

y w

ater

act

ivity

. Cer

eal F

oods

Wor

ld. 2

6(7)

:345

-349

.

Chen

, H.C

. (19

95).

Seaf

ood

micr

oorg

anism

s an

d se

afoo

d sa

fety.

Jour

nal o

f Foo

d an

d D

rug

Ana

lysis.

3:1

33-1

44.

Farb

er,

J.M.,

F. Co

ates

, an

d E.

Dale

y. (1

992)

. M

inim

um

wate

r act

ivity

requ

irem

ents

for t

he g

row

th o

f List

eria

mon

o-cy

toge

nes.

Lette

rs In

App

lied

Micr

obio

logy

. 15:

103-

105.

Aqu

aLab

5. T

he M

enus

26

The

audi

ble

alarm

can

be

turn

ed o

ff co

mpl

etel

y, it

can

beep

mom

enta

rily

whe

n th

e sa

mpl

e is

finish

ed a

nd t

hen

stop

, or i

t can

bee

p co

ntin

uous

ly un

til th

e kn

ob is

turn

ed

to th

e O

PEN

/LO

AD

pos

ition

.

EXIT

You

may

pre

ss th

e E

XIT

but

ton

(the

low

er le

ft bu

tton)

to

exit

back

to th

e m

ain m

easu

rem

ent s

cree

n at

any

tim

e.

Adj

ustin

g fo

r lin

ear

offs

etW

hen

you

need

to a

djus

t for

line

ar o

ffset

, pre

ss th

e up

per

right

but

ton

in t

he s

yste

m c

onfig

urat

ion

men

u, a

nd y

ou

will

be

brou

ght t

o th

e lin

ear o

ffset

men

u. F

or m

ore

deta

ils

on li

near

offs

et a

nd h

ow t

o ve

rify

for

it, p

lease

ref

er t

o Ch

apte

r 7.

AquaLab

13. Further Reading

72

in foods. Critical Reviews in Food Science and N

utrition. 36(5):465-513.

Franks, F. (1982). Water activity as a m

easure of biological viability

and quality

control. Cereal

Foods W

orld. 27(9):403-407.

Franks, F. (1991). Water activity: a credible m

easure of food safety and quality? Trends in Food Science and Tech-nology. M

arch:68-72.

Hardm

an, T.M. (1988). W

ater and Food Quality. E

lseiver Press, London.

Kress-Rogers, E

. (1993). Food quality measurem

ent. Food Industry N

ews. Septem

ber:23-26.

Levine, H. and L. Slade. (1991). W

ater Relationships in Foods. Plenum

Press, New

York.

Mannheim

, C.H., J.X

. Liu, and S.G. G

ilbert. (1994). Con-trol of w

ater in foods during storage. Journal of Food E

ngineering. 22:509-532.

McM

eekin, T.A. and T. Ross. (1996). Shelf life prediction:

Status and future possibilities. International Journal of Food M


Nelson, K

.A. and T.P. Labuza. (1994). W

ater activity and

AquaLab

6. Cleaning and M

aintenance

27

6. Cleaning and Maintenance

Keeping your A

quaLab clean is vital to maintaining the

accuracy of your instrument. D

ust and sampling debris

can contaminate the sam

pling chamber and m

ust there -fore be regularly cleaned out. To clean your instrum

ent, carefully follow

these instructions and refer to the labeled diagram

below..

View of inside block chamber

PurposeThe purpose for the cleaning procedure is to rem

ove grease, dirt and other soluble substances w

hich can

thermopile

mirror

optical sensor

chamber fan

Aqu

aLab

13. F

urth

er Re

adin

g

71

(199

4).

Pred

ictio

n of

wat

er a

ctiv

ity i

n fo

od s

yste

ms:

A

com

pute

r pr

ogra

m f

or p

redi

ctin

g w

ater

act

ivity

in m

ulti-

com

pone

nt fo

ods.

Revi

sta

Esp

anol

a D

e Ci

encia

Y T

ecno

-lo

gia

De

Alim

ento

s. 34

:427

-440

.

Vos,

P.T.

and

T.P

. Lab

uza.

(197

4). T

echn

ique

for m

easu

re-

men

ts o

f w

ater

act

ivity

in t

he h

igh

a w r

ange

. Jou

rnal

of

Agr

icultu

ral a

nd F

ood

Chem

istry

. 22:

326-

327.

Voys

ey, P

. (19

93).

An

evalu

atio

n of

the A

quaL

ab C

X-2

sys-

tem

for

mea

surin

g w

ater

act

ivity

. D

iges

t, M

icrob

iolo

gy

Sect

ion.

124

Foo

d Q

uali

ty a

nd S

afe

tyBr

andt

, L. (

1996

). Bo

und

for

succ

ess.

Cont

rolli

ng w

ater

ac

tivity

giv

es t

echn

olog

ists

the

edge

in

deve

lopi

ng s

afe,

shelf

-sta

ble

food

s. Fo

od F

orm

ulat

ing.

Sept

embe

r:41-

48.

Chiri

fe, J

. and

B.M

. Del-

Pilar

. (19

94).

Wat

er a

ctiv

ity, g

lass

trans

ition

and

micr

obial

sta

bilit

y in

con

cent

rate

d/se

mi-

moi

st fo

od sy

stem

s. Jo

urna

l of F

ood

Scien

ce. 5

9:92

1-92

7.

Chiri

fe,

J. an

d M

.P.

Buer

a. (1

995)

. A

crit

ical

revi

ew o

f so

me

non-

equi

libriu

m s

ituat

ions

and

glas

s tra

nsiti

ons

on

wat

er a

ctiv

ity v

alues

of

food

s in

the

micr

obio

logi

cal

grow

th ra

nge.

Jour

nal o

f Foo

d E

ngin

eerin

g. 25

:531

-552

.

Chiri

fe,

J. an

d M

.P.

Buer

a. (1

996)

. W

ater

act

ivity

, w

ater

gl

ass d

ynam

ics, a

nd th

e co

ntro

l of m

icrob

iolo

gica

l gro

wth

Aqu

aLab

6. C

lean

ing

and

Mai

nten

ance

28

abso

rb/r

eleas

e w

ater

dur

ing

verif

icatio

n, c

alibr

atio

n, a

nd/

or sa

mpl

e te

stin

g. F

or a

smoo

th a

nd e

ven

dew

form

atio

n,

it re

quire

s the

mirr

or to

be p

erfe

ctly

clea

n. I

f the

re ar

e any

co

ntam

inan

ts (e

.g. fi

nger

prin

ts) o

n th

e mirr

or, t

he d

ew w

ill

form

une

venl

y and

thus

affe

ct th

e acc

urac

y of t

he re

adin

g.

Mat

eria

ls N

eede

d

•A

thin

plas

tic ro

d or

oth

er n

on-m

etal

impl

emen

t

•D

istill

ed W

ater

•Is

opro

pyl A

lcoho

l (IP

A) o

r Dec

agon

Clea

ning

Sol

utio

n

•K

imw

ipes

®

You

may

also

pur

chas

e th

e A

quaL

ab C

leani

ng K

it w

hich

co

mes

with

all

the

abov

e m

ater

ials

exce

pt t

he I

sopr

opyl

A

lcoho

l and

Dist

illed

Wat

er.

NO

TE: W

ash

your

han

ds w

ith so

ap a

nd w

ater

and/

or u

se cle

an

lab gl

oves

befor

e sta

rting

the c

leanin

g pr

ocedu

re.

This

will

preve

nt

oils f

rom

conta

mina

ting t

he cl

eani

ng m

ateri

als, t

he sa

mple

cham

ber

and/

or th

e sen

sors.

Cle

ani

ng t

he B

lock

and

Sen

sors

Acc

essi

ng th

e Bl

ock

Turn

the

pow

er o

ff on

you

r A

quaL

ab (

switc

h in

bac

k.)

Nex

t, re

mov

e th

e ca

se li

d sc

rew

loca

ted

on th

e ba

ck p

anel.

Ca

refu

lly r

emov

e th

e lid

by

pulli

ng t

he b

ack

of t

he l

id

upw

ard

and

then

slid

ing

the

lid b

ack

(aw

ay fr

om th

e fr

ont

AquaLab

13. Further Reading

70

Troller, J.A. and J.H

.B. Christian. (1978). Water A

ctivity and Food. A

cademic Press, N

ew York.

Troller, J.A. and V.N

. Scott. (1992). Measurem

ent of water

activity (aw ) and acidity. In: Compendium

of Methods for

the Microbiological E

xamination of Foods. Vanderzant, C.

and D.F. Splittstoesser (ed.) A

merican Public H

ealth Asso -

ciation, Washington, D

.C. pp. 135-151.

Van den Berg, C. (1985). Water activity. In: Concentration

and Drying of Foods. M

acCarthy, D. (ed.) E

lsevier, Lon-don. pp. 11-35.

Van den Berg, C. (1991). Food-water relations: Progress

and integration, comm

ents and thoughts. In: Water Rela-

tionships in Foods. Levine, H. and L. Slade (ed.) Plenum

Press, N

ew York.

Van den Berg, C. and Bruin. (1981). Water activity and its

estimation in food system

s: Theoretical aspects. In: Water

Activity: Influences on Food Q

uality. Rockland, L.B. and G

.F. Stewart (ed.) A

cademic Press, N

ew York. pp. 1-61.

Vega, M.H

. and G.V. Barbosa-Canovas. (1994). Prediction

of water activity in food system

s: A review

on theoretical m

odels. Revista Espanola D

e Ciencia Y Tecnologia D

e A

limentos. 34:368-388.

Vega, M.H

., B. Romanach, and G

.V. Barbosa-Canovas.

AquaLab

6. Cleaning and M

aintenance

29

of the case) and off. Unscrew

the two thumbscrew

s that secure the sensor block. U

nplug the cable with the 20-pin

socket that attaches the block to the main circuit board by

releasing the two locking levers that are on either side of the socket. Carefully lift the block straight up from

its m

ount. Turn the block over to expose the chamber cavity

as shown in the illustration at the beginning of this chapter.

NO

TE for V

olatiles Block: If cleaning an AquaLab Series 3 V

ol-atiles Block, follow the cleaning procedures listed below being espe-cially careful not to get cleaning solution or alcohol on the capacitance sensor filter. Repeated exposure of cleaning materials or contami-nants to the filter may cause inaccurate readings. If the filter appears contaminated, replace it while being careful not to disturb the sensor behind the filter.

Clea

ning Pro

cedure:

Cleaning your AquaLab is a m

ulti-step procedure which

involves washing, rinsing, and drying for each specific area

as outlined below:

1. Clea

ning the Sa

mp

le Cha

mb

erN

ote: Be extremely careful not to damage the fan blades (see illus-tration) when cleaning the chamber.

a.Rem

ove any debris that may have collected w

ithin or around the sam

ple chanber.

b.W

rap a NE

W K

imw

ipe around the end of the thin

Aqu

aLab

13. F

urth

er Re

adin

g

69

Roa,

V. a

nd M

.S.

Tapi

a de

Daz

a. (1

991)

. E

valu

atio

n of

w

ater

act

ivity

mea

sure

men

ts w

ith a

dew

poi

nt e

lectro

nic

hum

idity

met

er. L

eben

smitt

el-W

issen

scha

ft un

d-Te

chno

l-og

ie. 2

4(3)

:208

-213

.

Roos

, K.D

. (19

75).

Est

imat

ion

of w

ater

activ

ity in

inte

rme-

diat

e m

oist

ure

food

s. Fo

od T

echn

olog

y. 29

:26-

30.

Scot

t, V.

N. a

nd D

.T. B

erna

rd. (

1983

). In

fluen

ce o

f tem

per-

atur

e on

the

mea

sure

men

t of

wat

er a

ctiv

ity o

f fo

od a

nd

salt

syst

ems.

Jour

nal o

f Foo

d Sc

ience

. 48:

552-

554.

Snav

ely, M

.J., J.

C. P

rice,

and

H.W

. Jun

. (19

90).

A co

mpa

rison

of

thre

e eq

uilib

rium

rela

tive

hum

idity

mea

surin

g de

vice

s. D

rug

Dev

elopm

ent a

nd In

dustr

ial P

harm

acy.

16(8

):139

9-14

09.

Stam

p, J

.A.,

S. L

insc

ott,

C. L

omau

ro,

and

T.P.

Labu

za.

(198

4). M

easu

rem

ent o

f wat

er ac

tivity

of s

alt so

lutio

ns an

d fo

ods b

y se

vera

l ele

ctro

nic

met

hods

as c

ompa

red

to d

irect

va

por

pres

sure

mea

sure

men

t. Jo

urna

l of

Foo

d Sc

ienc

e. 49

:113

9-11

42.

Stol

off,

L. (1

978)

. Cali

brat

ion

of w

ater

act

ivity

mea

surin

g in

stru

men

ts a

nd d

evice

s: Co

llabo

rativ

e st

udy.

Jour

nal o

f A

ssoc

iatio

n of

Offi

cial A

naly

tical

Chem

ists.

61:1

166-

1178

.

Trol

ler,

J.A.

(198

3).

Met

hods

to

mea

sure

wat

er a

ctiv

ity.

Jour

nal o

f Foo

d Pr

otec

tion.

46:

129-

134.

Aqu

aLab

6. C

lean

ing

and

Mai

nten

ance

30

plas

tic r

od (

spat

ula)

and

moi

sten

it

with

iso

prop

yl alc

ohol

or

Dec

agon

Clea

ning

Sol

utio

n.

Not

e: D

o N

OT

dip

a us

ed K

imw

ipe

into

you

r con

tain

er o

f IPA

or

clea

ning

sol

utio

n (th

e IP

A o

r clea

ning

sol

utio

n w

ill

beco

me

cont

amin

ated

).

c.W

ASH

--Clea

n all

sur

face

edg

es o

f the

sam

ples

cha

m-

ber

incl

udin

g th

e ed

ge w

here

the

sam

ple

cup

seals

to

the c

ham

ber b

lock

. Yo

u m

ay n

eed

to re

plac

e the

Kim

-w

ipe

if it

beco

mes

too

dirty

dur

ing

this

proc

ess.

d.RI

NSE

--Rep

eat

step

s b

and

c us

ing

new

Kim

wip

es

with

dist

illed

wat

er.

e.D

RY--R

epea

t ste

ps b

and

c u

sing

new,

dry

Kim

wip

es

to h

elp r

emov

e an

y m

oist

ure

rem

ainin

g fr

om t

he

clean

ing.

f.V

isuall

y in

spec

t th

e sa

mpl

e ch

ambe

r fo

r cle

anlin

ess.

Re-c

lean

if ne

cess

ary.

Note

: D

o not

reuse

Kimw

ipes.

2.

Clea

n th

e M

irro

r

a.W

rap

a ne

w K

imw

ipe

arou

nd th

e en

d of

the

thin

plas

-tic

rod

(spa

tula)

and

moi

sten

it w

ith is

opro

pyl a

lcoho

l or

Dec

agon

Clea

ning

Sol

utio

n.

b.W

ASH

--Sw

ipe

the

moi

sten

ed K

imw

ipe

acro

ss t

he

mirr

or o

nce.

(A

sin

gle

swip

e is

usua

lly s

uffic

ient

to

rem

ove

cont

amin

ants.

)

c.RI

NSE

--Rep

eat s

teps

a-b

usin

g ne

w K

imw

ipes

moi

sted

with

dist

illed

wat

er in

stead

of c

leani

ng so

lutio

n.

AquaLab

13. Further Reading

68

Karm

as, E. (1981). M

easurement of m

oisture content. Cereal Foods W

orld. 26(7):332-334.

Kitic, D

., D.C. Pereira-Jardim

, G. Favetto, S.L. Resnik, and

J. Chirife. (1986). Theoretical prediction of the water activ-

ity of standard saturated salt solutions at various tempera-

tures. Journal of Food Science. 51:1037-1042.

Labuza, T.P. and R. Contreras-Medellin. (1981). Prediction

of moisture protection requirem

ents for foods. Cereal Foods W

orld. 26(7):335-343.

Labuza, T.P., K. A

cott, S.R. Tatini, and R.Y. Lee. (1976). W

ater activity determination: A

collaborative study of dif-ferent m

ethods. Journal of Food Science. 41:910-917.

Prior, B.A. (1979). M

easurement of w

ater activity in foods: A

review. Journal of Food Protection. 42(8):668-674.

Reid, D.S. (1976). W

ater activity concepts in intermediate

moisture foods. In: Interm

ediate Moisture Foods.

Davies, R., G

.G. Birch, and K

.J. Parker (ed.) Applied Sci-

ence Publishers, London. pp. 54-65.

Richard, J. and T.P. Labuza. (1990). Rapid determination

of the water activity of som

e reference solutions, culture m

edia and cheese using a new dew

point apparatus. Sci -ences des A

liments. 10:57-64.

AquaLab

6. Cleaning and M

aintenance

31

d.D

RY--Repeat steps a-b using new, dry Kim

wipes to

help remove any m

oisture remaining from

the cleaning.

e.V

isually inspect the mirror for cleanliness. Re-clean if

necessary.

3. Clean the Therm

opile a

nd Optica

l Sensor

a.W

rap a new K

imw

ipe around the end of the thin plas-tic rod (spatula) and m

oisten it with isopropyl alcohol

or Decagon Cleaning Solution.

b.W

ASH

--Swipe the m

oistened Kim

wipe across ther-

mopile and optical sensor. (A

single swipe is usually

sufficient to remove contam

inants.)

c.RIN

SE--Repeat steps a-b using new

Kim

wipes m

oist-ened w

ith distilled water instead of cleaning solution.

d.D

RY--Repeat steps a-b but use a new, dry Kim

wipe to

help remove any m

oisture remaining from

the cleaning.

e.V

isually inspect the thermopile and optical sensor for

cleanliness. Re-clean if necessary.

4. A

dd

itiona

l Dry

ing Tim

e

a.V

isually inspect the sample cham

ber and sensors for contam

inants, including moisture. If necessary, repeat

the cleaning process using new K

imw

ipes.

b.Let stand for about 5 m

inutes to ensure the sample

chamber is dry.

Aqu

aLab

13. F

urth

er Re

adin

g

67

13. F

urth

er R

ead

ing

Wat

er A

ctiv

ity

Theo

ry &

Mea

sure

men

tBo

usqu

et-R

icard

, M, G

. Qua

lyle,

T. P

harm

, and

J.C.

Che

f-te

l. (1

980)

. Com

para

tive

stud

y of

thre

e m

etho

ds o

f det

er-

min

ing

wat

er a

ctiv

ity i

n in

term

ediat

e m

oist

ure

food

s. Le

bens

mitt

el-W

issen

scha

ftund

-Tec

hnol

ogie.

13:1

69-1

73.

Chiri

fe,

J., G

. Fa

vetto

, C.

Fer

ro-F

onta

n, a

nd S

. Re

snik

. (1

983)

. The

wat

er a

ctiv

ity o

f sta

ndar

d sa

tura

ted

salt

solu

-tio

ns in

the

rang

e of

inte

rmed

iate

moi

stur

e fo

ods.

Lebe

ns-

mitt

el-W

issen

scha

ft un

d-Te

chno

logi

e. 16

:36-

38.

Duc

kwor

th,

R. (

1975

). W

ater

Rela

tions

of

Food

s. A

ca-

dem

ic Pr

ess,

New

Yor

k.

Gom

ez-D

iaz, R

. (19

92).

Wat

er a

ctiv

ity in

food

s: D

eter

mi-

natio

n m

etho

ds. A

limen

taria

. 29:

77-8

2.

Góm

ez, R

. and

Fer

nand

ez-S

algue

ro J.

(199

2). W

ater

act

iv-

ity a

nd c

hem

ical

com

posit

ion

of s

ome

food

em

ulsio

ns.

Food

Che

mist

ry. 4

5:91

-93.

Gre

ensp

an, L

. (19

77).

Hum

idity

fixe

d po

ints

of b

inar

y sa

tu-

rate

d aq

ueou

s sol

utio

ns. J

ourn

al of

Res

earc

h of

the

Nat

iona

l Bu

reau

of S

tand

ards

- A.

Phys

ics an

d Ch

emist

ry. 8

1A:8

9-96

.

Aqu

aLab

6. C

lean

ing

and

Mai

nten

ance

32

Che

ckin

g C

ali

bra

tio

nA

fter

you

have

clea

ned

the

cham

ber

and

othe

r pa

rts o

f yo

ur A

quaL

ab, i

t is

impo

rtant

to

chec

k th

e in

stru

men

t’s

perf

orm

ance

in o

rder

to c

orre

ct fo

r any

line

ar o

ffset

that

m

ay h

ave

occu

rred

dur

ing

the

clean

ing

proc

ess.

Befo

re y

ou c

heck

the

inst

rum

ent w

e re

com

men

d th

at y

ou

run

a sa

mpl

e of

the

activ

ated

cha

rcoa

l pell

ets

prov

ided

in

your

Aqu

aLab

clea

ning

kit.

Thi

s cle

ans

the

air in

side

the

cham

ber,

help

ing

it co

me

back

to a

sta

ble

sam

plin

g en

vi-

ronm

ent.

Verif

y th

e lin

ear

offs

et a

gain

st k

now

n ca

libra

tion

stan

-da

rds

acco

rdin

g to

the

pro

cedu

re d

escr

ibed

in

the

next

ch

apte

r. If

a lin

ear o

ffset

has

occ

urre

d, re

fer t

o “a

djus

t for

lin

ear

offs

et”

sect

ion

in C

hapt

er 7

for

dire

ctio

ns o

n ho

w

to c

orre

ct fo

r lin

ear o

ffset

. If,

afte

r adj

ustin

g fo

r lin

ear o

ff -se

t, yo

ur in

stru

men

t is

still

not

rea

ding

sam

ples

cor

rect

ly,

plea

se c

onta

ct D

ecag

on fo

r sup

port.

AquaLab

12. Support and Repair

66

Rep

air C

osts

Manufacturer’s defects and instrum

ents within the three-

year warranty w

ill be repaired at no charge. Non-w

arranty repair charges for parts, labor and shipping w

ill be billed to you. A

n extra fee may be charged for rush work.

Decagon

will

provide an

estimated

repair cost,

if requested.

Loa

ner Service

Decagon has loaner instrum

ents to keep you measuring

water activity w

hile your instrument is being serviced. If

your AquaLab is still under calibration w

arranty or you have a service plan w

ith your instrument, there is no

charge for the loaner service.

AquaLab

7. Verification and C

alibration

33

7. Verification and Calibration

It is important to verify A

quaLab’s water activity calibra-

tion against known standards to guarantee optim

al perfor-m

ance and accuracy. Decagon recom

mends verification

daily, once per shift, or before each use (if used infre-quently).

Wa

ter Activ

ity V

erificatio

nA

quaLab uses the chilled-mirror dew

point technique to determ

ine water activity. Because this is a prim

ary mea-

surement of relative hum

idity, no calibration is necessary; how

ever, it is important to check for linear offset periodi-

cally. The components used by the instrum

ent to measure

water activity are subject to contam

ination which m

ay affect the A

quaLab’s performance. W

hen this occurs, it changes the accuracy of the instrum

ent. This is what is

called a “linear offset.” Therefore, frequent verification assures you that your A

quaLab is performing correctly.

Linear offset is checked by using two different calibration standards.

Ca

libra

tion Sta

nda

rds

Calibration standards are specially prepared salt solutions having a specific m

olality and water activity constant

which are accurately m

easurable. The calibration standards

Aqu

aLab

12. S

uppo

rt an

d Re

pair

65

2.Pl

ace

an e

mpt

y sa

mpl

e cu

p in

the

sam

ple

draw

er t

o he

lp p

rote

ct it

from

dam

age

durin

g sh

ippi

ng.

3.Pl

ace

the

Aqu

aLab

in a

plas

tic b

ag to

avo

id d

isfig

urin

g m

arks

from

the

pack

agin

g.

4.D

on’t

sh

ip t

he

pow

er c

ord

or

seri

al c

able

.

5.If

the

orig

inal

pack

agin

g is

not a

vaila

ble,

pack

the

box

mod

erat

ely ti

ght w

ith p

acki

ng m

ater

ial (e

.g. s

tyro

foam

pe

anut

s or

bub

ble

wra

p), e

nsur

ing

the

inst

rum

ent

is su

spen

ded

in th

e pa

ckin

g m

ater

ial.

6.In

clude

a c

opy

of t

he R

MA

for

m i

n th

e sh

ipm

ent.

Plea

se v

erify

the

ship

to a

nd b

ill to

info

rmat

ion,

con

-ta

ct n

ame,

and

prob

lem d

escr

iptio

n.

If a

nyth

ing

is in

corr

ect,

plea

se c

orre

ct it

on

the

RMA

form

or c

on-

tact

a D

ecag

on re

pres

enta

tive.

7.Ta

pe th

e bo

x in

bot

h di

rect

ions

for a

dded

supp

ort.

8.In

clude

the

RMA

num

ber i

n th

e at

tent

ion

line

on th

e sh

ippi

ng la

bel.

Ship

to:

Dec

agon

Dev

ices I

nc.

ATTN

: RM

A (i

nser

t you

r RM

A #

)23

65 N

E H

opki

ns C

ourt

Pullm

an, W

A 9

9163

Aqu

aLab

7. V

erifi

catio

n and

Cal

ibra

tion

34

that

wer

e se

nt w

ith y

our i

nitia

l shi

pmen

t are

ver

y ac

cura

te

and

read

ily a

vaila

ble

from

Dec

agon

. U

sing

calib

ratio

n st

anda

rds t

o ve

rify

accu

racy

can

grea

tly re

duce

pre

para

tion

erro

rs. F

or th

ese

reas

ons,

we

reco

mm

end

usin

g st

anda

rds

avail

able

thro

ugh

Dec

agon

for t

he m

ost a

ccur

ate

verif

ica-

tion

of y

our A

quaL

ab’s

perf

orm

ance

.

Perfo

rman

ce C

alibr

atio

n St

anda

rds

com

e in

fiv

e wa

ter

activ

ity le

vels:

1.0

00, 0

.984

, 0.7

60, 0

.500

, and

0.2

50a w

. Th

e sta

ndar

ds a

re p

rodu

ced

unde

r a

strict

qua

lity

assu

ranc

e re

gim

e. P

lease

cont

act D

ecag

on D

evice

s to

orde

r add

ition

al sta

ndar

ds v

ia sa

les@

deca

gon.

com

or 1

-800

-755

-275

1.

NO

TE:

If

you

need

to

obta

in a

Mat

erial

Safet

y D

ata

Sheet

(M

SDS)

for a

ny of

these

stan

dard

s, a

prin

table

versi

on is

ava

ilable

on

our w

ebsit

e at w

ww.de

cago

n.com

/msd

s.

To u

se a

cali

brat

ion

stan

dard

, rem

ove

the

twist

top

and

Cal

ibra

tion

Stan

dard

@

25°C

Wat

er A

ctiv

ity

Dis

tille

d W

ater

1.00

0 ±0

.003

0.5m

KC

l0.

984

±0.0

03

6.0m

NaC

l0.

760

±0.0

03

8.57

m L

iCl

0.50

0 ±0

.003

13.4

1m L

iCl

0.25

0 ±0

.003

AquaLab

12. Support and Repair

64

12. Sup

po

rt and

Rep

air

NO

TE: If you purchased your A

quaLab from one of our interna-tional distributors, please contact them. They will be able to provide you with local support and service.

When encountering problem

s with your A

quaLab (that can’t be resolved w

ith the help of this manual), please con-

tact Decagon Custom

er Support at [email protected]

, 800-755-2751 (U

S and Canada), 509-332-2756 (Interna-tional) or fax us at (509) 332-5158. Please have the serial num

ber and model of the instrum

ent ready.

All A

quaLabs returning to Decagon for servicing m

ust be accom

panied with a Return M

aterial Authorization (RM

A)

form. Prior to shipping the instrum

ent, please contact a D

ecagon customer support representative to obtain an

RMA

.

Shipp

ing D

irections:

The following steps w

ill help to ensure the safe shipping and processing of your A

quaLab.

1.Ship your A

quaLab in its original cardboard box with

suspension packaging. If this is not possible, use a box that has at least 4 inches of space betw

een your instru -m

ent and each wall of the box.

AquaLab


alibration

35

pour the contents into an AquaLab sam

ple cup. If for som

e reason you cannot obtain Decagon’s calibration

standards and need to make a saturated salt solution for

verification, refer to Appendix A

.

Ca

libra

tion

When to Verify for Linear O

ffsetLinear offset should be checked against two know

n cali-bration standards either daily, once per shift or before each use. Linear offset should never be verified solely against distilled w

ater, since it does not give an accurate representation of the linear offset. For batch processing, the instrum

ent should be checked regularly against a know

n standard of similar w

ater activity. It is also a good idea to check the offset w

ith a standard of similar w

ater activity w

hen the general water activity range of your sam

-ple is changing. Checking the w

ater activity of a standard solution w

ill alert you to the possibility of unit contamina-

tion or shifts in the linear offset from other causes.

Note: The calibration process is the same for both the dewpoint and

volatiles block except that the accuracy for the capacitance sensor in the volatiles block is ±

0.015 aw .

VerificationTo verify for linear offset of your AquaLab, do the following:1.

Choose a calibration standard that is close to the water

activity of the sample you are m

easuring. Note: The

AquaLab needs to warm up for approximately 15 minutes to

make accurate readings.

Aqu

aLab

11. T

roub

lesh

ootin

g

63

volta

ge, i

n un

its o

f m

illiv

olts.

Thi

s va

lue

shou

ld n

orm

ally

be b

etw

een

400

and

2400

mV,

and

shou

ld b

e st

eady

.

You

can’

t cha

nge

anyt

hing

in th

is sc

reen

, but

it is

her

e to

gi

ve y

ou a

n in

dica

tion

of th

e co

mpo

nent

per

form

ance

. If

you

notic

e th

at a

ny o

f th

ese

valu

es a

re n

ot w

hat

they

sh

ould

be,

cont

act D

ecag

on fo

r fur

ther

inst

ruct

ion.

Pre

ss

the

butto

n ne

xt t

o -Exit-

to

get

back

to

the

main

m

enu.

Aqu

aLab

7. V

erifi

catio

n and

Cal

ibra

tion

36

2.E

mpt

y a

vial

of th

e ch

osen

cali

brat

ion

stan

dard

into

a

sam

ple

cup

and

plac

e it

in t

he A

quaL

ab’s

sam

ple

draw

er.

Mak

e su

re th

at yo

ur st

anda

rd is

as c

lose

to th

e in

stru

men

t tem

pera

ture

as p

ossib

le.

Note

: M

ake s

ure t

he ri

m of

the s

ample

cup

is cle

an.

3.Ca

refu

lly sl

ide

the

draw

er c

lose

d an

d tu

rn th

e kn

ob to

th

e RE

AD

pos

ition

.

4. T

ake

two

read

ings

. The

wat

er a

ctiv

ity re

adin

gs sh

ould

be

with

in ±

0.0

03a w

of t

he g

iven

valu

e fo

r the

cali

bra-

tion

stan

dard

. See

App

endi

x B

for

the

corr

ect

wat

er

activ

ity v

alue

of D

ecag

on’s

stan

dard

s at

tem

pera

ture

s ot

her t

han

25°C

.

5.If

your

Aqu

aLab

is re

adin

g w

ithin

±0.

003a

w o

f the

cal-

ibra

tion

stan

dard

, cho

se a

sec

ond

calib

ratio

n st

anda

rd

that

wou

ld b

orde

r the

rang

e of

wat

er a

ctiv

ity y

ou p

lan

to t

est.

For

exa

mpl

e, if

you

plan

to

test

for

wat

er

activ

ity re

adin

gs ra

ngin

g be

twee

n 0.

713

and

0.62

1 yo

u sh

ould

use

the

6.0M

, NaC

l (0.

76a w

) sta

ndar

d fo

r you

r fir

st v

erifi

catio

n an

d th

e 8.

57M

LiC

l (0.

50a w

) fo

r th

e se

cond

ver

ifica

tion.

6.Pr

epar

e a

sam

ple

cup

of th

e se

cond

cali

brat

ion

stan

-da

rd a

nd m

ake

two

read

ings

. The

wat

er a

ctiv

ity r

ead-

ing

for

the

seco

nd c

alibr

atio

n st

anda

rd s

houl

d be

w

ithin

±0.

003a

w.

AquaLab

11. Troubleshooting

62

Co

mp

onent Perfo

rma

nce ScreenIf, after cleaning your instrum

ent and reading the other troubleshooting hints, you have reason to believe that one of the com

ponents of your AquaLab m

ay be causing mea-

surement error, you can access a screen that w

ill display values for com

ponent performance. This is done either by

holding down the low

er right button while turning on the

instrument, or by first pressing the low

er left button (sys-tem

configuration menu), then the upper right button (lin-

ear offset menu) and then the upper left button.

The following screen w

ill appear:

This screen gives you four values. The top left value is the value the therm

ocouple is reading. It is basically the differ-ence in tem

perature between the block and the m

irror. It should typically have a value of 3, ±

0.3. If this is zero, there is som

ething wrong w

ith the thermocouple. The top

right value is the value read by the thermopile, w

hich is the tem

perature difference between the block and what it

“sees” below it (the sam

ple, when reading). This value

should be around zero, but will change w

hen you change the draw

er position. The bottom left value is the block

temperature. This value should be around am

bient tem-

perature. The bottom right value is the m

irror reflectance

-Exit-

sensors

3.21 0.030

23.5 1100

AquaLab


alibration

37

7.If either one of the verifications is not correct, it is probably due to contam

ination of the sensor chamber.

For cleaning instructions, see Chapter 6. After clean-

ing, repeat verification from step two.

8.If you are consistently getting readings outside the w

ater activity of your first calibration standard by m

ore than ±0.003aw , a linear offset has probably

occurred. In this case, adjust the reading on the cali-bration standard to its correct value as outlined in the next section.

Adjusting for Linear O

ffset

1.O

nce you are certain that a linear offset has occurred, enter the system

configuration menu by pressing the

lower left button from

the measurem

ent screen. Press the upper right button in the system

configuration m

enu to enter the linear offset menu. You w

ill be guided through the linear offset routine.

2.If you w

ish to continue, press the button next to “yes.” To return to the m

easurement screen, press the button

next to “no.” After selecting “yes,” the follow

ing screen w

ill appear:

place standard

in drawer and read

Aqu

aLab

11. T

roub

lesh

ootin

g

61

PRO

BLEM

#9

:T

he

follo

win

g sc

reen

com

es u

p a

fter

tu

rnin

g on

th

e m

ach

ine:

SOLU

TIO

NS:

1)T

he

blo

ck i

s n

ot p

lugg

ed i

n t

o th

e m

oth

erb

oard

. O

pen

the

case

and

che

ck to

mak

e su

re th

at th

e sm

all

ribbo

n ca

ble

that

con

nect

s th

e bl

ock

to t

he m

othe

r -bo

ard

is sn

appe

d an

d lo

cked

in p

lace.

2)O

ne

or

mor

e co

mp

onen

ts

has

fa

iled

on

th

e b

lock

’s

circ

uit

b

oard

. If

th

e bl

ock

is pr

oper

ly pl

ugge

d in

to

the

mot

herb

oard

and

thi

s m

essa

ge

appe

ars,

it is

likel

y th

at o

ne o

r m

ore

of t

he c

ompo

-ne

nts

have

fail

ed o

n th

e bl

ock’s

circ

uit

boar

d. I

f yo

u pr

ess

-exi

t- at

thi

s pr

ompt

, the

inst

rum

ent

will

not

ha

ve v

alues

for

the

com

pone

nt th

at h

as f

ailed

, whi

ch

will

lead

to in

corr

ect r

eadi

ngs.

If th

is m

essa

ge a

ppea

rs

and

you

cont

inue

to sa

mpl

e, D

ecag

on c

anno

t be

liabl

e fo

r err

ors i

n re

adin

g th

at m

ay o

ccur

. Con

tact

Dec

agon

fo

r a so

lutio

n to

this

prob

lem.

block failure

Aqu

aLab

7. V

erifi

catio

n and

Cal

ibra

tion

38

3.E

mpt

y th

e w

hole

vial

of a

cali

brat

ion

stan

dard

into

a

sam

ple

cup.

W

e re

com

men

d us

ing

the

6.0M

NaC

l (0

.76a

w).

Do

not

adju

st f

or t

he o

ffset

usin

g di

still

ed

wat

er.

Ens

ure

the

rim a

nd o

utsid

e of

the

cup

are

cle

an.

Pl

ace

the

prep

ared

sa

mpl

e cu

p in

th

e A

quaL

ab’s

sam

ple

draw

er.

NO

TE: T

he sa

me ca

libra

tion

stand

ard

may b

e used

to v

erify

and

adjus

t the

line

ar of

fset.

4.Cl

ose

the

draw

er, b

eing

espe

cially

car

eful

so

the

solu

-tio

n wo

n’t s

plas

h or

spi

ll an

d co

ntam

inat

e th

e ch

am-

ber.

5.Tu

rn th

e dr

awer

kno

b to

the

REA

D p

ositi

on to

mak

e a

wat

er a

ctiv

ity re

adin

g.

Note

: If y

ou d

ecide

at t

his p

oint n

ot to

contin

ue w

ith th

e lin

ear o

ffset

prog

ram,

just

retur

n th

e kno

b to

the O

PEN

/LOA

D p

ositio

n an

d rem

ove t

he sa

mple.

Afte

r you

r Aqu

aLab

has

fini

shed

sam

plin

g th

e ca

libra

tion

stan

dard

, it w

ill d

isplay

the

follo

win

g sc

reen

:

0.760 adjust +

exit -

use

thes

e bu

tton

s to

adj

ust t

he v

alue

AquaLab

11. Troubleshooting

60

PRO

BLEM #8:

A sm

all triangle ap

pears in

the u

pp

er right corn

er after sam

plin

g:

SOLU

TION

:

1)T

he m

irror need

s to be clean

ed, along with the rest

of the sample cham

ber, or a volatile contaminant is

interfering with the dew

point determination. This tri-

angle is a mirror perform

ance indicator. The perfor-m

ance of the mirror is m

easured on a 0 to 1 scale, with

1 being the cleanest. When the A

quaLab senses that the m

irror performance has dropped to unacceptable

levels, it will display the triangular w

arning sign after the sam

ple has been measured. To see w

hat the mir-

ror performance value is, press the upper right button

when the triangle appears, and it w

ill show you the

value. At this point, you should stop sam

pling and clean the cham

ber. If the triangle is still on the screen after cleaning, the m

irror is most likely still dirty or a

volatile in your sample is contam

inating the mirror.

Contact Decagon for m

ore assistance.

0.853 a

w24.7°C

AquaLab


alibration

39

6.A

djust the water activity value to its proper value for

the particular calibration standard you are measuring

by pressing the up or down buttons until the correct

value is displayed. When the value is correct, press the

Exit button to store this new

value.

Note: This is the only menu where these buttons can change the lin-

ear offset, so you won’t hurt anything by pressing these buttons in other menus.

7.Re-m

easure the calibration standard again in the nor-m

al sampling m

ode. It should read the proper value at a given tem

perature for that calibration standard (see A

ppendix B).

8.M

easure the water activity of a second calibration

standard according

to the

verification procedure

described above. If both verification readings are w

ithin ±0.003aw then the instrum

ent is ready to begin testing.

If you still have incorrect verification readings after clean-ing the cham

ber and/or adjusting for linear offset, contact D

ecagon for

further instructions

at support@

deca-gon.com

or 1-800-755-2751 or 509-332-2756. If you pur-chased your A

quaLab from one of our international

distributors, please contact them for local service and sup-

port.

Aqu

aLab

11. T

roub

lesh

ootin

g

59

this

mes

sage

will

com

e up

. Ess

entia

lly, i

t m

eans

tha

t th

ere

is no

t eno

ugh

sam

ple

moi

stur

e to

con

dens

e on

th

e m

irror

and

pro

vide

a re

adin

g.

2)T

he

mir

ror

may

be

dir

ty.

Try

clean

ing

the

mirr

or

and

cham

ber a

nd m

easu

ring

the

sam

ple

again

.

PRO

BLEM

#6

:M

essa

ge o

n s

cree

n d

isp

lays

“a

w >

1.0

....”

SOLU

TIO

N:

Th

e C

oole

r is

dam

aged

an

d w

ill n

eed

to

be

serv

iced

b

y D

ecag

on.

See

Ch

apte

r 12

for

det

aile

d in

stru

ctio

ns.

PRO

BLEM

#7

:V

erif

icat

ion

is n

ot c

orre

ct.

SOLU

TIO

NS:

1)

T

he

sam

ple

ch

amb

er

and

m

irro

r n

eed

to

b

e cl

ean

ed.

See

Cha

pter

6 fo

r det

ailed

cle

anin

g in

stru

c-tio

ns.

If v

erifi

catio

n is

still

not

cor

rect

, the

n lin

ear o

ff-

set h

as o

ccur

red.

2) V

erif

y an

d A

djus

t for

Lin

ear

Off

set.

Afte

r you

hav

e cle

aned

the s

ampl

e cha

mbe

r and

mirr

or (C

hpt.

6) yo

u wi

ll ne

ed to

use

a Ca

libra

tion

Stan

dard

to ve

rify a

nd ad

just

for

Line

ar O

ffset

as d

escr

ibed

in C

hapt

er 7

.

Aqu

aLab

7. V

erifi

catio

n and

Cal

ibra

tion

40

This

flowc

hart

is a

graph

ical r

epres

enta

tion

of th

e dir

ection

s giv

en

abov

e for

check

ing f

or li

near

offse

t.

AquaLab

11. Troubleshooting

58

PRO

BLEM #4

:M

essage on screen

disp

lays the follow

ing:

SOLU

TION

:

1)Y

our sam

ple’s tem

perature is

too high

for the

instrum

ent to equilibrate w

ith it in a reasonable am

ount of time. The instrum

ent and sample need to

be in temperature equilibrium

before accurate samples

can be made. Therefore, very cold sam

ples will take a

very long time to m

easure for the same reason. To

avoid this problem, m

ake sure to only measure sam

ples that are at the sam

e temperature as the instrum

ent.

PRO

BLEM #5:

Message on

screen d

isplays th

e “<“ sym

bol.

SOLU

TION

:

1)T

he sam

ple is too d

ry for the instrument to read

accurately. If your sample has a w

ater activity that is less than below

the detection limits of the instrum

ent,

sample too hot

aw < 0.02824.7 °C

AquaLab

8. Sample Preparation

41

8. Sam

ple Prep

ara

tion

Your AquaLab w

ill continually provide accurate water

activity measurem

ents as long as its internal sensors are not contam

inated by improperly-prepared sam

ples. Care -ful preparation and loading of sam

ples will lengthen tim

e betw

een cleanings and will help you avoid cleaning and

downtim

e.

Prepa

ring the Sa

mp

leTo prepare a sam

ple, follow these steps:

1.M

ake sure th

at the sam

ple to be m

easured

is h

omogen

eous. M

ulti-component sam

ples (e.g., muf-

fins with raisins) or sam

ples that have outside coatings (like deep-fried, breaded foods) can be m

easured, but m

ay take longer to equilibrate. For samples like these,

AquaLab m

ay take more than five m

inutes to give an accurate reading, or m

ay require multiple readings of

the same sam

ple. Measuring the w

ater activity of these types of product is discussed in detail later in this chapter (see M

aterials Needing Special Preparation).

2.P

lace the sam

ple in

a disp

osable sam

ple cu

p, com

pletely coverin

g the b

ottom of th

e cup, if p

os-sib

le. AquaLab is able to accurately m

easure a sample

that does not (or cannot) cover the bottom of the cup.

Aqu

aLab

11. T

roub

lesh

ootin

g

57

dens

e on

the

sur

face

of

the

chill

ed m

irror

and

alte

r re

adin

gs. P

lease

refe

r to

the

volat

iles

sect

ion

in C

hap-

ter 8

for h

ints

on

redu

cing

diffi

culti

es w

ith m

easu

ring

sam

ples

with

pro

pylen

e gl

ycol

. If

you

hav

e fu

rther

qu

estio

ns re

gard

ing

the

mea

sure

men

t of v

olat

iles c

on-

tact

Dec

agon

.

4)A

fan

bla

de

in t

he

blo

ck c

ham

ber

may

be

bro

ken

or

ben

t. I

f eve

n sa

lt st

anda

rds t

ake

a lo

ng ti

me

to

read

, and

the s

ampl

e cha

mbe

r is c

lean,

you

may

hav

e a

brok

en c

ham

ber f

an b

lade.

This

is es

pecia

lly li

kely

if yo

u ha

ve ju

st c

leane

d th

e ch

ambe

r. If

you

susp

ect t

his

may

hav

e ha

ppen

ed, c

onta

ct D

ecag

on fo

r det

ails o

n re

plac

emen

t.

PRO

BLEM

#3

:W

ater

act

ivit

y re

adin

gs o

n c

alib

rati

on s

tan

dar

ds

are

too

hig

h/

low

an

d a

lin

ear

offs

et a

dju

stm

ent

can

not

b

e m

ade

any

hig

her

/lo

wer

.

SOLU

TIO

N:

1)T

he

ther

mop

ile in

you

r ch

amb

er, w

hic

h m

easu

res

sam

ple

tem

per

atu

re,

may

hav

e b

ecom

e co

nta

mi -

nat

ed. R

efer

to C

hapt

er 6

for d

irect

ions

on

clean

ing.

2)T

he

cham

ber

mir

ror

may

be

dir

ty. R

efer

to C

hapt

er

6 fo

r dire

ctio

ns o

n cle

anin

g.

Aqu

aLab

8. S

ampl

e Pr

epar

atio

n

42

For e

xam

ple,

raisi

ns o

nly

need

to b

e pl

aced

in th

e cu

p an

d no

t flat

tene

d to

cov

er th

e bo

ttom

. A la

rger

sam

ple

surf

ace

area

incr

ease

s ins

trum

ent e

fficie

ncy

by p

rovi

d-in

g m

ore

stab

le in

frar

ed s

ampl

e te

mpe

ratu

res.

It als

o sp

eeds

up

the

read

ing

by s

horte

ning

the

time

need

ed

to re

ach

vapo

r equ

ilibr

ium

.

3.D

o n

ot f

ill t

he

sam

ple

cu

p m

ore

than

hal

f fu

ll.

Ove

rfill

ed c

up

s w

ill c

onta

min

ate

the

sen

sors

in

th

e se

nso

r ch

amb

er!

Filli

ng th

e sa

mpl

e cu

p w

ill n

ot

mak

e th

e re

adin

gs fa

ster

or m

ore

accu

rate

. The

re o

nly

need

s to

be

enou

gh s

ampl

e in

the

cup

to

allow

the

w

ater

in th

e sa

mpl

e to

equ

ilibr

ate

with

the

wat

er in

the

vapo

r ph

ase

and

not c

hang

e th

e m

oist

ure

cont

ent o

f th

e sa

mpl

e. Th

ere

is a

min

imum

am

ount

of

sam

ple

need

ed; t

here

fore

, cov

erin

g th

e bo

ttom

of t

he s

ampl

e cu

p is

norm

ally

enou

gh.

4.M

ake

sure

th

at t

he

rim

and

ou

tsid

e of

th

e sa

mp

le

cup

are

cle

an. W

ipe

any

exce

ss sa

mpl

e m

ater

ial fr

om

the

rim o

f the

cup

with

a c

lean

tissu

e. M

ater

ial le

ft on

th

e rim

or t

he o

utsid

e of

the

cup

will

con

tam

inat

e th

e se

nsor

cha

mbe

r an

d be

tra

nsfe

rred

to

subs

eque

nt

sam

ples

. The

rim

of

the

cup

form

s a

vapo

r se

al w

ith

the

sens

or b

lock

whe

n th

e dr

awer

kno

b is

turn

ed t

o th

e RE

AD

pos

ition

. The

refo

re, a

ny s

ampl

e m

ater

ial

left

on t

he c

up r

im w

ill b

e tra

nsfe

rred

to

the

bloc

k,

prev

entin

g th

is se

al an

d co

ntam

inat

ing

futu

re sa

mpl

es.

AquaLab

11. Troubleshooting

56

Caution: D

o not use any other kind of fuse or you will

risk damage to your instrum

ent as well as void your

warranty.

c. Replace the fuse-holder and push it into the fuse-w

ell until the release tab snaps in place.

d. Re-connect the power cord and turn your instru-

ment on. If the fuse blow

s again, a failed component

may be causing the problem

. Contact Decagon to

make arrangem

ents for repairs.

PRO

BLEM #2

:R

eadin

gs are slow or in

consisten

t.

SOLU

TION

:

1)T

he sam

ple ch

amb

er may b

e dirty. Refer to Chap-

ter 6 of the manual for directions on cleaning the sam

-ple cham

ber.

2)Som

e prod

ucts ab

sorb or d

esorb m

oisture very

slowly, causing m

easurements to take longer than

usual, and nothing can be done to speed up the pro-cess. Refer to Chapter 8 for further explanation.

3)Y

our sam

ple m

ay contain

volatiles. Volatiles are know

n to cause unstable readings, because they con-

AquaLab


43

5.If a sam

ple w

ill be read

at some oth

er time, p

ut

the sam

ple cu

p’s d

isposab

le lid on

the cu

p to

restrict water tran

sfer. For long-term storage, seal

the lid by placing tape or Parafilm

completely

around the cup/lid junction. It is necessary to seal the cup if it w

ill be a long time before the m

easurement is

made.

Sam

ples N

eeding

Specia

l Prep

ara

tion

AquaLab reads m

ost materials in less than five m

inutes, depending on w

hich mode you are operating in. Som

e sam

ples, however, m

ay require longer reading times, due

to the nature of the material you are sam

pling. These m

aterials need additional preparation to ensure quick, accurate readings. To find out w

hether special sample

preparation is necessary, take a reading and see how long it

takes to find the water activity. If it takes longer than six

minutes, rem

ove the sample and take a reading of a cali-

bration standard. This will ensure that the sam

ple itself is causing the long read tim

e, and that there is not a problem

with your instrum

ent. If the calibration standard also takes longer than six m

inutes to sample, refer to Chapter 11 of

this manual for m

ore information.

Coated and D

ried Samples

Samples w

ith coatings such as sugar or fat often require longer reading tim

es, because it takes longer for them to

equilibrate. If this is the case for your samples, don’t worry

Aqu

aLab

11. T

roub

lesh

ootin

g

55

Tro

ub

lesh

ooti

ng

Qu

ick

Gu

ide

(con

tinu

ed)

If th

is pr

oblem

occ

urs:

Refe

r to:

Scre

en d

isplay

s “a

w>

1.0”

......

......

......

......

......

...Pr

oblem

#6

Verif

icat

ion

not c

orre

ct...

......

......

......

......

......

....P

robl

em #

7

Trian

gle

appe

ars i

n up

per r

ight

cor

ner..

......

....P

robl

em #

8

Scre

en d

isplay

s “Bl

ock

failu

re”

......

......

......

......

Prob

lem #

9tu

rnin

g on

Aqu

aLab

PRO

BLEM

#1:

Aq

uaL

ab w

on’t

tu

rn o

n.

SOLU

TIO

N:

1)C

hec

k to

mak

e su

re y

our

pow

er c

ord

is

secu

rely

at

tach

ed to

the

back

of t

he in

stru

men

t and

it is

plu

g-gi

ned

into

the

pow

er o

utlet

.

2)A

pow

er s

urg

e m

ay h

ave

cau

sed

a fu

se t

o b

low

. To

chan

ge th

e fu

ses,

follo

w th

ese

inst

ruct

ions

:

a. U

nplu

g th

e po

wer

cor

d .

b. L

ocat

e th

e pa

nel w

here

the

pow

er c

ord

plug

s in

. Th

e fu

se b

ox is

on

the

right

side

of t

hat p

anel

. Pre

ss in

on

the

relea

se ta

b an

d pu

ll th

e fu

se-h

olde

r ou

t. P

ull

the

brok

en f

use(

s)ou

t an

d re

plac

e w

ith a

1.2

5 A

mp

250V

fuse

.

Aqu

aLab

8. S

ampl

e Pr

epar

atio

n

44

that

som

ethi

ng is

wro

ng w

ith y

our

inst

rum

ent;

it sim

ply

mea

ns th

at y

our p

artic

ular

sam

ple

take

s lo

nger

than

mos

t to

equ

ilibr

ate

wat

er w

ith it

s out

side

envi

ronm

ent.

To re

duce

the

time

need

ed to

take

a w

ater

act

ivity

read

ing

for c

oate

d or

drie

d sa

mpl

es, o

ne th

ing

you

can

do is

cru

sh,

slice

, or

grin

d th

e sa

mpl

e be

fore

put

ting

it in

the

sam

ple

cup.

Thi

s in

crea

ses

the

surf

ace

area

of

the

sam

ple,

thus

de

crea

sing

read

ing

times

. K

eep

in m

ind,

how

ever

, th

at

mod

ifyin

g so

me

sam

ples

may

alte

r th

eir w

ater

act

ivity

re

adin

gs.

For e

xam

ple,

a can

dy m

ay h

ave

a sof

t cho

colat

e ce

nter

and

a ha

rd o

uter

coa

ting.

The

wat

er a

ctiv

ity r

eadi

ng f

or t

he

cent

er a

nd t

he o

uter

coa

ting

are

diffe

rent

, so

one

woul

d ne

ed t

o ev

aluat

e w

hich

par

t of

the

sam

ple

need

ed t

o be

m

easu

red

befo

re c

rush

ing

it. W

hen

the

cand

y is

crus

hed,

fo

r ex

ampl

e, th

e w

ater

act

ivity

will

rep

rese

nt th

e av

erag

e w

ater

act

ivity

of

the

entir

e sa

mpl

e; w

here

as l

eavi

ng t

he

cand

y w

hole

will

giv

e a

read

ing

for t

he c

oatin

g, w

hich

may

ac

t as a

bar

rier t

o th

e ce

nter

.N

ote: i

f you

crus

h, gri

nd, o

r slic

e you

r sam

ple, b

e con

sisten

t in

the

meth

od yo

u us

e in

orde

r to o

btain

repr

oduc

ible r

esults

.

Slow

Wat

er-E

mitt

ing

Sam

ples

Som

e ex

trem

ely

dry,

dehy

drat

ed, h

ighl

y vi

scou

s w

ater

-in-

oil

(but

ter),

hig

h fa

t, or

glas

sy c

ompo

sitio

ns m

ay h

ave

incr

ease

d re

ad ti

mes

, due

to th

eir m

oist

ure

sorp

tion

char

-ac

teris

tics.

Aqu

aLab

may

req

uire

up

to t

en m

inut

es t

o

AquaLab

11. Troubleshooting

54

11. Troub

leshoo

ting

AquaLab is a high perform

ance instrument, designed to

have low m

aintenance and few problem

s if used with care.

Unfortunately, som

etimes even the best operators using

the best

instruments

encounter technical

difficulties. Below

is quick reference guide that will direct you to

detailed solutions of some problem

s that may occur. If

these remedies still don’t resolve your problem

, then please contact D

ecagon for help (see Chapter 12: Support and Repair).T

roub

leshootin

g Qu

ick Gu

ide

If this problem occurs:

Refer to:

AquaLab won’t turn on

.....................................Problem #

1

Readings are slow or inconsistent....................Problem

#2

Water activity readings on solutions are..........Problem

#3

too high/low to adjust

Screen displays “Sample too hot”.................. Problem

#4

Screen displays “aw <

x.xxx”..........................Problem #

5

AquaLab


45

reach an accurate measurem

ent of water activity and noth-

ing can be done to decrease the reading times of these

types of samples.

For faster reading, it is important to have the w

ater activity of the cham

ber at or below the w

ater activity of these type of sam

ples. This causes the sample to release w

ater to the vapor phase and equilibrate w

ith the chamber. If the w

ater activity of the headspace is greater than this type of sam

-ple, a long period of tim

e will be required to reach equilib-

rium and the w

ater activity of the sample m

ay be affected.

Volatile Samples

AquaLab w

ill give accurate readings on most sam

ples. H

owever, sam

ples with certain volatiles in high enough

concentrations may give inaccurate w

ater activity values. This is because the volatiles condense on the m

irror dur-ing the reading process, but do not evaporate from

the m

irror as water does. A

s a result, the reading on volatiles w

ill not be accurate. The concentration of volatiles that w

ill cause interference is variable and matrix dependent.

The most effective m

ethod to determine if volatiles are a

problem is to look for incorrect standard readings after

reading the sample.

If you will be testing sam

ples with volatiles on a regular

basis that need a more accurate reading, you should con -

sider upgrading to the Decagon’s Series 4TE

V w

hich is designed for m

easuring volatiles such as propylene glycol

Aqu

aLab

10. C

ompu

ter I

nter

face

53

Aqu

aLin

k scr

een

Usi

ng W

ind

ow

s H

yp

erte

rmin

al

To u

se H

yper

term

inal

with

you

r A

quaL

ab, f

ollo

w t

hese

st

eps:

1.Pr

ess t

he S

tart

butto

n an

d se

lect P

rogr

ams >

Acc

esso

-rie

s > H

yper

term

inal

and

click

on

the

Hyp

erte

rmin

al ico

n.

2.A

t the

pro

mpt

, cho

ose

a na

me

for t

his p

rogr

am

(Aqu

aLab

is a

goo

d on

e) a

nd c

hoos

e an

arb

itrar

y ico

n ab

ove

to re

pres

ent i

t. In

futu

re d

ownl

oads

, you

will

be

able

to c

lick

on th

is ico

n in

hav

e it

alrea

dy se

t up

for

you

to d

ownl

oad.

Clic

k th

e O

K b

utto

n.

Aqu

aLab

8. S

ampl

e Pr

epar

atio

n

46

and

etha

nol.

For

mor

e in

form

atio

n ab

out

the

Serie

s 4T

EV,

co

ntac

t D

ecag

on

Dev

ices

at

supp

ort@

deca

-go

n.co

m o

r 1-8

00-7

55-2

751

or 5

09-3

32-2

756.

Low

Wa

ter

Act

ivit

ySa

mpl

es th

at h

ave

a w

ater

act

ivity

of l

ess

than

abo

ut 0

.03

cann

ot b

e ac

cura

tely

mea

sure

d w

ith th

e no

rmal

Aqu

aLab

Se

ries

3 m

odel.

Sam

ples

with

suc

h lo

w w

ater

act

ivity

val-

ues a

re ra

re. W

hen

a sa

mpl

e’s w

ater

act

ivity

valu

e is

belo

w

its a

bilit

y to

acc

urat

ely m

easu

re, y

our A

quaL

ab w

ill d

isplay

an

err

or m

essa

ge in

dica

ting

the

last r

eadi

ng it

cou

ld m

ake

on th

at p

artic

ular

sam

ple.

For

exam

ple,

say

you

are

mea

-su

ring

a dr

y sa

mpl

e an

d th

e fo

llow

ing

scre

en a

ppea

rs:

This

scre

en in

dica

tes t

hat t

he la

st w

ater

activ

ity re

adin

g th

e A

quaL

ab m

easu

red

on t

his

sam

ple

was

0.0

31 a

t 24

.7°C

. Th

eref

ore,

the

actu

al w

ater

act

ivity

of t

he s

ampl

e is

low

er

than

the

inst

rum

ent’s

com

pone

nts c

an m

easu

re.

If yo

ur s

ampl

e is

not

extre

mely

dry

but

is s

till g

ettin

g th

e er

ror m

essa

ge, r

efer

to C

hapt

er 1

1 fo

r oth

er p

ossib

le ex

plan

a -tio

ns.

Sam

ples

not

at R

oom

Tem

pera

ture

Sam

ples

tha

t ar

e 4

degr

ees

cold

er o

r w

arm

er t

han

the

inst

rum

ent (

cham

ber)

tem

pera

ture

will

nee

d to

equ

ilibr

ate

aw < 0.031

24.7 °C

AquaLab

10. Com

puter Interface

52

10. Co

mp

uter Interface

Your AquaLab w

as shipped to you with a standard RS-232

interface cable. Using this, you can use your com

puter’s term

inal program to send w

ater activity data to your com-

puter for further analysis and storage.

Aq

uaLink

Softw

are

An optional program

that is available for use with your

AquaLab is A

quaLink. AquaLink is a W

indows-based pro-

gram designed for collection and graphing of data from

all A

quaLab models. It logs w

ater activity, temperature, tim

e of m

easurement, and a tim

e and date stamp (from

your com

puter's clock). It also has sample identification and

comm

ents fields that you can use to help annotate the data that your A

quaLab is taking. AquaLink takes the data and

displays it in a real-time graph. You can control the incre-

ments of each axis to custom

ize the graph as you wish. If

you are interested in purchasing a copy of AquaLink, con -

tact Decagon or your authorized distributor. H

ere is a sam

ple picture of the AquaLink program

:

AquaLab


47

to ambient tem

perature before a fast, accurate reading can be m

ade. Rapid changes in temperature over short periods

of time w

ill cause the water activity readings to rise or fall

until the temperature stabilizes. W

hen the temperature sta -

bilizes within one or two degrees of the cham

ber tempera-

ture, you can proceed with norm

al measurem

ents.

High-w

ater activity samples that are w

armer than the

chamber tem

perature can cause condensation inside the m

easuring chamber, w

hich will adversely affect subse-

quent readings. A w

arning message appears (S

ample

too hot

) if the sample tem

perature is more than 4°C

above chamber tem

perature. If this message appears,

imm

ediately remove the sam

ple from the instrum

ent, place a lid on the cup, and allow

the sample to cool to

within 4°C of the instrum

ent before measuring.

Samples that are low

er than 4°C of the instrument’s tem

-perature w

ill cause long read times. The sam

ple tempera-

ture must be w

ithin one or two degrees of the chamber

temperature before fast, accurate readings can be m

ade.

Aqu

aLab

9. T

akin

g a

Read

ing

51

that

th

e m

irro

r h

as b

ecom

e to

o d

irty

to

give

acc

u-

rate

mea

sure

men

ts,

and

you

nee

d t

o cl

ean

th

e m

irro

r an

d c

ham

ber

bef

ore

con

tinu

ing

to s

amp

le.

For

mor

e d

etai

ls a

bou

t th

is s

ymb

ol, p

leas

e re

fer

to

Ch

apte

r 11

. F

or

clea

nin

g in

stru

ctio

ns,

re

fer

to

Ch

apte

r 6.

•If

a s

amp

le h

as a

wat

er a

ctiv

ity

low

er t

han

ab

out

0.03

, A

qu

aLab

will

dis

pla

y a

mes

sage

, ac

com

pa -

nie

d b

y th

e fl

ash

ing

ligh

t, n

otif

yin

g yo

u t

hat

you

r sa

mp

le i

s to

o d

ry t

o b

e ac

cura

tely

mea

sure

d b

y th

e A

qu

aLab

. Fol

low

ing

is a

n e

xam

ple

:

Th

is m

essa

ge w

ill s

tay

on t

he

scre

en u

nti

l yo

u o

pen

th

e sa

mp

le d

raw

er.

If y

ou k

now

th

at y

our

sam

ple

’s

wat

er a

ctiv

ity

is a

bov

e w

hat

th

e sc

reen

is

telli

ng

you

, yo

ur

inst

rum

ent’s

sen

sors

may

hav

e b

een

con

tam

i -n

ated

an

d w

ill n

eed

to

be

clea

ned

(se

e C

hap

ter

6) o

r se

rvic

ed (

see

Ch

apte

r 12

).

aw < 0.031

24.7 °C

Aqu

aLab

9. T

akin

g a

Read

ing

48

9. T

ak

ing

a R

ead

ing

Mea

sure

men

t St

eps

Onc

e yo

u ha

ve p

repa

red

your

sam

ple,

you

are

read

y to

ta

ke re

adin

gs. T

he p

roce

ss is

sim

ple:

1.Tu

rn t

he s

ampl

e dr

awer

kno

b to

the

OPE

N/L

OA

D

posit

ion

and

pull

the

draw

er o

pen.

2.Pl

ace

your

pre

pare

d sa

mpl

e in

the

draw

er. C

heck

the

top

lip o

f the

cup

to m

ake

sure

it is

free

from

sam

ple

resid

ue (

rem

embe

r, an

ove

r-fill

ed s

ampl

e cu

p m

ay

cont

amin

ate

the

cham

ber’s

sens

ors)

.

3.Ca

refu

lly sl

ide

the

draw

er c

lose

d, b

eing

espe

cially

car

e-fu

l if y

ou h

ave

a liq

uid

sam

ple

that

may

spl

ash

or s

pill

and

cont

amin

ate

the

cham

ber.

4.Tu

rn th

e sa

mpl

e dr

awer

kno

b to

the

REA

D p

ositi

on

to s

eal t

he s

ampl

e cu

p w

ith th

e ch

ambe

r. Th

e fo

llow

-in

g sc

reen

will

app

ear:

This

will

sta

rt th

e re

ad c

ycle.

Le

ngth

of

read

tim

es

chamber sealed

measurementstarted

AquaLab

9. Taking a Reading

50

•T

ake special care n

ot to move th

e samp

le draw

er too

qu

ickly w

hen

load

ing

or u

nload

ing

liqu

id

samp

les, in ord

er to avoid sp

illing.

•If a sam

ple h

as a temp

erature th

at is four d

egrees

high

er (or more) th

an th

e Aq

uaL

ab’s ch

amb

er, th

e instru

men

t will d

isplay a m

essage (below

)

alerting you

to cool the sam

ple b

efore readin

g. A

lthou

gh

the

instru

men

t w

ill m

easure

warm

er sam

ples, th

e readin

gs may b

e inaccu

rate. Warm

sam

ples can

cause con

den

sation in

the ch

amb

er if th

ey have a h

igh w

ater activity.

•T

he

physical

temp

erature

of th

e in

strum

ent

shou

ld b

e betw

een 4°- 50°C

. Betw

een th

ese amb

i-en

t temp

eratures, A

qu

aLab

will m

easure sam

ples

of similar tem

peratu

re qu

ickly and

accurately.

•If you

are samp

ling an

d a trian

gular w

arnin

g sym-

bol ap

pears in

the top

right corn

er, this in

dicates

sample too hot

0.853 a

w24.7°C

AquaLab

9. Taking a Reading

49

may

vary depending

on tem

perature differences

between the cham

ber and your sample, and other

properties of your sample.

Note: Samples that have a large difference in water activity from

previous samples may need extra time to reach equilibrium, since some of the previous sample’s atmosphere stays in the chamber after measurement.

Ho

w A

qua

Lab

tak

es Rea

ding

sA

quaLab’s reading cycle continues until the rate of change of three consecutive readings are less than 0.0005 of each other. The instrum

ent crosses the dew threshold num

er-ous tim

es to ensure the accuracy of readings. When the

instrument has finished its read cycle, the w

ater activity is displayed, accom

panied by the LED

flash and beeper (if you have the beeper enabled).

Ca

utions

•N

ever leave a samp

le in you

r Aq

uaL

ab after a

readin

g has b

een taken

. Th

e samp

le may sp

ill and

con

tamin

ate th

e in

strum

ent’s

cham

ber

if th

e in

strum

ent is accid

entally m

oved or jolted

.

•N

ever try to move your instrum

ent after a sample has

been loaded. Movem

ent may cause the sam

ple mate -

rial to spill and contaminate the sam

ple chamber.

b Series 3 6 al - manuals.decagon.commanuals.decagon.com/Retired and Discontinued... · AquaLab Lab...

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