Evaluation of the QA forms used for

deposition analyses

EU/UN ECE - International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests________________________________________________________________

Working Group on QA/QC in Laboratories

Meeting of the Heads of the Laboratories

Zadar, Croatia, 19-20 September 2013

Aldo Marchetto, Gabriele Tartari & Rosario Mosello,

C.N.R. Institute of Ecosystem Study, Verbania (Italy)

e-mail: r.mosello@ise.cnr.it

http://www.ise.cnr.it/it/verbania-it/home-vb http://www.idrolab.ise.cnr.it/

Aims of the presentation

Since 2009 it is mandatory to include the information on

analytical methods and laboratory QA in the trasmission of

atmospheric deposition results.

Methods (source of information)

Since 2009 it is mandatory to include the information on

analytical methods and laboratory QA in the trasmission of

atmospheric deposition results.

Aims of the presentation

Taking account of the different analytical techniques, the

presentation will focus on anomalous reported values (e.g. for

LOQs) and missing or wrong information, which highlight

problems in the laboratories or in the transmission of data.

5

Aldo Marchetto, Gabriele Tartari & Rosario Mosello

Limit of Detection (LOD)and

Limit of Quantification (LOQ)

estimation and use in the chemical lab

Life+ FutMon - Working Group on QA/QC in Laboratories

Meeting of the Heads of the Laboratories

C.N.R. Institute of Ecosystem Study, Verbania (Italy)

e-mail: a.marchetto@ise.cnr.it http://www.iii.to.cnr.it

12-13 October 2009 in Warsaw

6

Internal and external QC

Ø calibration

Ø blank control charts

Ø mean control charts

Ø LOD & LOQ

Ø result validation using ion balance andconductivity check

u Internal quality control

u External quality control

Ø use of certified standard

Ø analyses of certified samples

Ø participation to WRTs

12-13 October 2009 in Warsaw

7

Why to estimate LOD and LOQ?

Ø To evaluate the suitability of the used

analytical technique and conditions to the

aims of the monitoring.

Ø To compare the quality of the determination

with other published results in order to

evaluate if there is necessity and possibility of

improvement.

12-13 October 2009 in Warsaw

8

Evaluation of LOD and LOQ

If you have mean control charts at different concentration,

use them to evaluate LOD and LOQ

else, if calibration slope is very stable (i.e. spectrophotometry)

use SD of the blanks (if possible)

or of a control sample of low concentration

or of the lowest standard used for calibration

else,

apply Hubax-Vos method,

or use the variability of the calibration standards

12-13 October 2009 in Warsaw

9

Statistics mg L-1

Average 0.508

Standard Deviation 0.013

Standard Deviation recommended 0.025

RSD % 2.7

RSD % recommended 5.0

Minimum 0.47

Maximum 0.54

N. data 115

0

5

10

15

20

25

0 1 2 3 4 5 6 7 8 9 10 11

mg L-1

R.S

.D.

Co

ntr

ol

Ch

art

s

Using control chart

Chloride

Ion Chromatography

C.N.R.- I.S.E.Verbania - Italy

0.40

0.42

0.44

0.46

0.48

0.50

0.52

0.54

0.56

0.58

0.601 6

11

16

21

26

31

36

41

46

51

56

61

66

71

76

81

86

91

96

101

106

111

mg

L-1

UWL

LWL

UCL

LCL

RSD = 3.37 (mg/L)-0.46

Single control chart in use

from Nov 2006 to Aug 2007

All control charts used in the lab for

IC determinations (in 20 years)

12-13 October 2009 in Warsaw

10

Conclusions

u Quality Control is an important tool to criticize analytical

activity, to improve it and to assure that it is suitable for

the purpose of monitoring.

u The estimation of LOD and LOQ is an important part of

Quality Control.

u LOD and LOQ can be simply evaluated using results of

control charts, blank samples or calibration curves.

u If you do not store these data yet, please store them

anywhere and in a few years you will have years of data...

12-13 October 2009 in Warsaw

LO

Qs

LOQs of mandatory variables

LOQs of mandatory variablesL

OQ

s

Strong outliers

Values of LOQ obtained in each laboratory

should be compared with those

suggested in Arcachon (2011)

LOQArcachon (2011)

Alkalinity 10 µeq/L

Conductivity 2 µS/cm

Cl- 0.2 mg/L

S-SO4= 0.1 mg/L

N-NO3- 0.08 mg/L

Total N 0.2 mg/L

LOQArcachon (2011)

Ca++ 0.1 mg/L

Mg++ 0.05 mg/L

Na+ 0.1 mg/L

K+ 0.4mg/L

N-NH4+ 0.08 mg/L

DOC 1 mg/L

P-PO4--- 0.1 mg/L

LOQs of mandatory variablesL

OQ

s

LOQs of mandatory variablesL

OQ

s

Other problems rising from the QA forms

v Only 38 labs out of 47 sent the quality form;

v Only 13 labs sent quality data for 13 mandatory variables

for 3 years.

Common errors:ØSame control chart for several years (is it an error?)

Ø Control chart mean < LOQ

Ø LOQ = 0

Ø Missing control chart for alkalinity, conductivity or pH

Ø Missing LOQ for alkalinity and conductivity (pH is OK)

Ø Wrong ring test number, or results from a ring test different

from the last one

Ø Wrong unit for optional metals (mg instead of µg)

Control chart mean < LOQ

LOQ = 0

Missing

control chart for:

alkalinity

conductivity

pH

Missing LOQ for:

alkalinity

conductivity

(pH is OK)

Wrong ring test

number,

or results from a

ring test different

from the last one

Correct WRT number:

3 for 2009

4 2010

5 2011

Mean values of the control charts

vs the deposition concentrations

wrong unit?

wrong unit?

Cd for example is correct!

1. Select CC mean values at least 3 times LOD, best around the

median of the measured values.

2. Populate CC with 2-4 measurement each day for at least 20 days.

3. Stabilize CC sample with chloroform (by acid to pH 4 for NH4+

and DOC).

Suggestions for an optimal use

of control charts

4. Use CC with different mean

concentrations in the next run, in

order to have at the end plots of

control chart R.S.D. vs CC mean0

5

10

15

20

25

0 1 2 3 4 5 6 7 8 9 10 11

mg L-1

R.S

.D. C

on

tro

l C

hart

s

All control charts used in the lab for

IC determinations (20 years !)

CC mean

Conclusions

üThe highest care is needed in the QA/QC practices and

documentation in the laboratory.

üThe comparison of LOD and other QC parameters among

laboratories gives information on the reliability of the

applied methods and the possibility of improvements.

üThe highest attention should be used in the transmission

of results and details on the methods and QA/QC, as

essential documentation for the evaluation of the quality

of data produced in the laboratory.

Thank you for your attention