Kinetic-Spectrophotometric Determination of Co (II) in Vegetable Samples by Using Indigo-Caramine

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64 | IJPR | July – September

International Journal of Pharmaceutical Research2012, Volume 4, Issue 3, 64-68

ISSN 0975-2366

Research Article

Kinetic-Spectrophotometric Determination of Co (II) in Vegetable Samples by Using Indigo-Caramine

B.Venkat Kiran, Somshankar Dubey and Battula Sreenivas Rao*

Department of Chemistry, GITAM Institute of Technology, GITAM University,Visakhapatnam –530045, A.P., India.

*Corresponding author E-mail ID: [email protected] Fax: +91-891-2790399

Received: 03/08/2011, Revised: 28/08/2011, Accepted: 17/09/2011

ABSTRACT

A new kinetic spectrophotometric method has been developed for the determination of trace Co (II) in effluent water. The

method is based on the catalytic effect of Co(II) on the oxidation of Indigo-caramine by potassium periodate in basicmedium. The concentration of Co(II) can be estimated spectrophotmetrically by measuring the decrease of absorbance of

analyte at 412 nm, using fixed time method. The influencing factors are investigated and optimum conditions are establishedas 0.70 ml of Indigo-caramine, 1.0ml of potassium-periodate, 4.0ml of 1M KOH at controlled -temperature of 25°C ± 5°C .

The proposed method allows the determination of Co (II) within the dynamic range of 0.01 ppm to 0.20 ppm. In theinterference study few cations and anions are known to interfere with the result. The proposed kinetic-catalytic method can

directly applied for the determination of Co (II) at trace levels in vegetable samples.

Key words: cobalt, kinetic spectrophotometry, indigo-caramine

INTRODUCTION

Cobalt is naturally occurring moderately toxic elementin comparison with other metals. Ambient water Quality

guidelines for Cobalt are reported [1]. This Sets Guidelinesfor Cobalt to protect Aquatic life in fresh water

Environment. Cobalt is a naturally occurring hard silver-grey metal that belongs to group nine of the periodic table.

It is a relatively rare element of the earth’s crust withconcentration around 25 mg/kg. As an integral part of the

vitamin B12 complex, cobalt is essential in trace amountsfor humans and animal life. The essentiality of cobalt has

also been demonstrated in the environment elsewhere: (a)

as a micronutrient for some blue-green algae, (b) required

for nitrogen-fixation in legumes, (c) in growth of manymarine algal species, including diatoms, chrysophytes and

dinoflagellates, and (d) in growth enhancement of some

terrestrial plants at low concentrations. However, in higher

concentrations, cobalt is toxic to humans and to terrestrialand aquatic animals and plants. Currently, cobalt is mainly

used in some types of steel and in a variety of alloys,

including high-temperature steel alloys, magnetic alloys,

and abrasion-resistant hard-facing alloys. Cobalt is used in

magnets to increase the saturation of magnetization of iron.It is also used as a pigment in glass, ceramics, and paints; as

paint drier; as a catalyst for the petroleum industry; and in

batteries. Many fertilizers are enriched with cobalt,

generally in the range of 1 mg/kg to 12 mg/kg, in order toamend cobalt-deficient agricultural soils. The concentration

of total cobalt in freshwaters is generally low (<1 µg/L).Higher concentrations are generally associated with

industrialized or mining areas. Concentrations of cobaltranging from non-detectable (detection limit 0.1 µg/L) to

27,000 µg/L have been measured; the total and dissolved in

ambient, uncontaminated environments are, however,

generally below 5 µg/L. Cobalt is also found in lowconcentration in marine waters. Municipal and industrial

wastes and effluents are primary sources of anthropogenic

cobalt in the environment. Anthropogenic emissions,

largely the burning of fossil fuels, account for 55% of all

cobalt in the air. Windborne soil particles and sea salt spray

are primary natural sources of cobalt to the atmosphere.The main method of analysis and determination of Co(II)

includes Flame atomic absorption spectroscopy (FAAS),Graphite furnace atomic absorption spectroscopy

(GFAAS), Inductively-coupled plasma optically emissionspectroscopy (ICP-OES).Inductively Coupled Plasma

coupled with Mass Detector (ICP-MS), these conventionaland hyphenated techniques can be applied after preliminary

treatments such as pre-concentration extraction which isnot only expensive and time-consuming, tedious and

practically difficult and needs a lot costly infrastructure and

technical know-how. Hence due to these reasons simple

colurometric methods are still popular. Catalytic-kineticmethod of high sensitivity equal to that of high end

hyphenated analytical techniques. The catalytic

spectrophotometric methods for the trace determination

offer three distinct advantages for achieving tracedetermination, because they have advantage such as

1) High sensitivity

2) Accuracy with simple procedure.

3) Less expensive apparatus.

In recently published articles, different analyticalmethods which are based on different analytical principles

such as Extractive Spectrophotmetry[2,3], Spectophotome-

try [4,5] Non-extractive derivative spectrophotmetry [6]

Cloud- point extraction [7], Graphite furnace Atomicadsorption Spectrophometry (GFAAS), Inductively coupled

plasma coupled with optically Emission Spectrophotmetry(ICP-OES)[8.9], Inductively coupled plasma coupled with

Atomic emission spectropmetry (ICP-AES), Inductivelycoupled plasma coupled with Mass spectrometry (ICP-MS),

Electro chemical detection (ECE) coupled with Liquid

chromatorgraphy [10] and kinetic spectrophotmetric

methods have been recognized as offering a valuableapproach for the trace analysis [11-15].The advantages of

catalytic-kinetic method is the fact that minimum and low

cost and easily available instruments such as pH-meter,

spectrophometer. Thermo-stat is required to achieve



sensitive, a

time.

Experimen

Cobalt stoc

263.0 mg o

Milli-Q woncentratio

Potassium

50.0m

of dissolve

Reagents a

Water: M

experiment

without an

1% Indigo

0.1025

and it is

alcohol. Sin

1M KOH:

5.6 g of KO

Apparatus

Absor

Model Vis

matching 1cwater Bath

used to mai

Fig 1: The

Reaction

The Cto the rate o

by determin

For the cat

At CKoH0.1 ppm.

Temperatur proportiona

For Uncat

At CKOH =

Temperatur

proportiona

for the esti

Battula e

curate and reli

tal

k solution

f Co (II) nitrat

ter. It is fuof Co (II) solu

eriodate Solu

of potassium

distilled water.

d Solutions

lli-Q water of

. All chemical

further purifica

Caramine Indi

g of Indigo car

issolved in100

ce it is unstable

H of AR grade

tion measurem

ible -25°C ±

m glass cells o(Kumar precisi

tain temperatu

ffect of Volum

echanism

ncentration of f reaction. The

ation of concen

alyzed reaction

-dc/dt = K1*

= 4.0ml,

e = 25°C ± 5°l to rate of catal

lyzed Reaction

-dc/dt =

4.0ml, CIN

e = 25°C ± 5°C

l to rate of un

ation of the a

t al / Internati

ble results in s

salt is dissolv

rther dilutedtion.

ion.

periodate is dis

erck male was

used are of AR

tion.

cator solution

aine is heated

ml of 1: 1

it is to be freshl

s dissolved in d

ents were mad

5°C Spectro

fixed wavelengon Bath Model:

e 25°C ± 5°C.

of 1M KOH

catalyst is direrate of the react

ration of cataly

s.:

KoH * CIND*C(

IND= 0.70

where K 1 is czed reaction.

:

o* CKoH * CIND

D = 0.70ml

, where K 1 is c

-catalyzed reac

ount of Co (II

nal Journal o

hort duration o

ed in 100 ml o

to get desire

solved in 100m

used for all th

Grade and use

at 80 °C for 1 h

ater and ethyl

y prepared.

istilled water.

using ELICO

hotmeter wit

th. A thermostaFour-tech) wa

tly proportionaon can be foun

t.

o(II)

l, CCo(II)

nstant which i

onstant which i

ion. Procedure

) and evaluatio

Pharmaceuti

f

f

l

r

-

-

t

l

of other p

17].

Fig 2:

Optimisa

The

was studie

F

Table2 V

Indigo-Ca

4.0ml of 1

Co

Results a

The Effec

Absorba

The

studied irecorded

FIG-2 an

change fr

hence1.0also obse

peridoate

reactions.very fast r as optimu

The Effec

The

the rangemaximum

optimumare record

al Research 2

arameters are Id

The effect of V

ion of Reactio

effect of differe

d in order to est

G-3-The effect

riation of Abso

ramine, 1.0ml o

M KOH

ncentration

Blank

0.01 ppm0.02 ppm

0.03 ppm0.05 ppm

0.10 ppm0.20 ppm

d Discussions

t of Volume of

ce.

nfluence of vo

the range of n the FIG-2 a

Table-4 that

m 0.40 to 1.0m

l is chosen for ved increasing

eyond 1.0 ml d

The fading of ate. Hence 1.0

value.

t of Volume of

nfluence of vol

of 3.0 ml of 4.at 4.0ml, hence

alue, for theed in the FIG-1

012 4(3) 64-6

IJPR | July

entical to those

olume of Potass

Conditions:

nt variables on

ablish optimum

of Volume of I

rbance at Fixed

f 500ppm of P

1200 Sec

0.7150

0.52000.4850

0.45000.4050

0.26500.0170

Potassium Per

ume of potassi

0.40 to 1.20mld Table-4. It

Absorbance in

and reached m

the measuremethe concentrat

rastically increa

the reaction of l of potassium

1M KOH on Δ

ume of 1M K

0 ml and Δ Ab4.0ml of 1M

easurement of and Table-6.

September |

given earlier [1

ium periodate

the reaction r

conditions.

ndicator.

time at 0.70 ml

tasium Perioda

∆1200

0.19500.2300

0.26500.3100

0.45000.6980

odate on Δ

m periodate

. The resultscan be seen fro

creases as volu

aximum at 1.0

nt of Co(II). Ition of potassi

ses the rate of t

reaction takes peridoate is fix

Absorbance.H was studied

sorbance reachOH was fixed

Co(II).The resu

5

6-

te

of

te,

as

rem

e

l ,

ism

he

ated

in

edas

lts



Battula et al / International Journal of Pharmaceutical Research 2012 4(3) 64-68


Table 1 Change of Absorbance at different concentration of Co(II),0.70ml 1% Indigo carmine, 4.0ml of 1M KOH,

1.0mml of 500ppm potassium periodate at fixed time interval

180S 360S 600S 720S 900S 1200S ∆180 ∆360 ∆600 ∆720 ∆900 ∆1200

Blank 1.046 0.881 0.840 0.779 0.737 0.715

0.01 0.919 0.831 0.720 0.712 0.600 0.520 0.127 0.050 0.120 0.067 0.137 0.195

0.02 0.795 0.706 0.610 0.592 0.512 0.485 0.251 0.175 0.230 0.187 0.225 0.230

0.03 0.651 0.578 0.540 0.532 0.510 0.450 0.395 0.303 0.300 0.247 0.227 0.265

0.05 0.573 0.508 0.480 0.442 0.432 0.405 0.473 0.373 0.360 0.337 0.305 0.3100.10 0.290 0.285 0.280 0.270 0.268 0.265 0.756 0.596 0.560 0.509 0.469 0.450

0.20 0.152 0.115 0.070 0.062 0.030 0.017 0.894 0.766 0.770 0.717 0.707 0.698

Correlation 0.930 0.94118 0.970 0.967 0.9897 0.9993

The Effect of Volume of Indicator on Δ Absorbance The influence of Volume of 1% indicator was studied

in the range of 0.60 to 0.75 ml. From FIG-3 and Table-5.The Δ Absorbance values reaches maximum at 0.70 ml

hence it is chosen as optimum value.

The Effect of Temperature on Δ Absorbance The effect of temperature was studied with other

experimental conditions being kept constant. The result

showed as temperature increases over 40 °C absorbance

values decreases and sensitivity also decreased. Whentemperature is within the range of 25°C ± 5°C , Δ absorbance reached as maximum hence it is taken as

optimum temperature.

Recommended Procedure: In the 10ml of stoppered

volumetric flask, 1.0ml of potassium periodate which actsas oxidant and 0.70ml of 1% Indigo caramine and 4.0ml of

1M KOH solution is added and gently shaken further it is

made upto to volume with distilled water. This is the

preparation of blank. Similarly 1.0ml of potassium periodate, 0.70ml of Indigo-caramine and 4.0ml of 1M

KOH solution of and required quantity of sample solutionof is added within the dynamic range 0.01ppm to 0.20 ppm

and made upto volume with distilled water. Simultaneously

stop watch is started, after the addition of last drop of

sample solution. After the required 1200sec the solutions blank and sample are absorbed gradually fades away.

Absorbance is measured at 412 nm. The difference in

absorbance of blank and sample directly used to find out

the concentration of Co (II) by using calibration plots. from

the above data, it is fixed as 1200 sec and 412 nm as

standards. It is also observed that kinetic data reflects that

Beers-Lamberts law and Correlation Equation andRegression Equation is obtained, in the dynamic range of

0.01ppm to 0.20ppm [16-17].

Calibration –Graph, Linearity and Detection Limits.

Under optimum experimental conditions 0.0, 0.01,

0.02, 0.03, 0.05, 0.10, 0.20 ppm of Co(II) was placed in the

calibrated volumetric volumetric flaks respectively. The

absorbance was measured against blank (water). The resultshowed that Linearity range 0.01 to 0.02 ppm.The Linearity Regressions Equation is

Regression Equation: y = 0.5353-2.62x

Sensitivity of the Method From above statistical data obtained from Table-1,

Slope (b), Intercept (a) and regression Equation is

formulated. The kinetic data of change in absorbance is

noted for different concentration of Co (II). The variation of

absorbance at fixed time interval with fixed concentrationof 1% Indigo caramine, IM KOH, 500 ppm of potassium

periodate.in Table –1. From Table-3 Limit of Quantification and Limit of

detection values are obtained

LOQ = 0.007 LOD = 0.002

Variation of absorbance at fixed time is represented inTable-2, from the statistical values obtained fixed time of

20 mins is fixed as optimum value.

Table-3 Limit of Quantification and Limit of Detection Obtained from Absorbance at Different Concentration of

Co(II) , 0.70ml of 1% Indicator Solution, 4.0ml of 1M KOH, 1.0ml of 500ppm of Oxidant

Concentration Ist IInd IIIrd Average Standard Deviation

0.01 0.522 0.525 0.5245 0.523833 0.001607

0.02 0.485 0.486 0.4868 0.485933 0.000902

0.03 0.45 0.452 0.458 0.453333 0.004163

0.05 0.405 0.408 0.401 0.404667 0.0035120.1 0.265 0.2653 0.267 0.265767 0.001079

0.2 0.017 0.0168 0.0175 0.0171 0.000361

Blank 0.715

Slope 2.629749Average Standard Deviation 0.001937

LOQ 0.007

LOD 0.002

Selectivity of the Method

Under of optimum conditions and Co (II) at 0.10 ppm

the effect of interfering ions was studied. The tolerancelimit of ions was fixed as the maximum relative error is not

great than 5% in the absorbance. It is tabulated in Table-7.

Regression Equation y= 0.5353-2.62x

Sample Preparation

Vegetable samples were purchased at a local

supermarket. Only edible parts were taken, washed withhigh-purity water cut and oven-dried at 85 °C for 24 h.

Next, they were ground in a household grinder for 10–20 s

and then in an agate mortar. All these operations must be




IJPR | July – September | 67

completed as expeditiously as possible, to avoiddegradation or/and contamination of the sample.

Table 4 Effect of Potassium Periodate at 0.70ml of 1%

Indigo Carmine, 4.0ml of 1M KOH, 0.1ppm of Co (II).

Blank 0.7055 ∆ Absorbance

0.40ml 0.2915 0.414

0.60ml 0.2825 0.4230.80ml 0.2758 0.42971.0ml 0.2652 0.4403

1.20ml 0.2649 0.4406

From Table-3 LOQ, LOD values are obtained.

From Table-4, effect of oxidizing Agent

From Table-5, effect of Indicator SolutionFrom Table-6, effect of 1M KOH solution is obtained.

From Table-7 effect of interference ions is obtained.

No sieving was needed. An SRM supplied by NIST, viz.,SRM 1572 (Citrus Leaves) was dried to a constant mass at

85 °C for 2 h, as per the supplier’s recommendations, and

used for method validation. Two sample preparation

procedures were used; blanks were also assayed in parallelin all instances. Dry Ashing : 0.2–0.3 g of dried vegetablewas accurately weighed in a platinum crucible and placed

in a muffle furnace and ashed at 600–650 °C overnight. The

fully ashed sample was dissolved with 2 ml of concentrated

HNO3 and evaporated to dryness in a sand-bath. Finally, the

residue was taken up in 10 ml of 0.2% v/v HNO 3.

Table 5 Effect of Volume of 1% Indigo Caramine at 4.0ml

of 1M KOH, 500ppm of Potassium Periodate Solution at

0.1ppm Concentration Co(II)


0.60ml 0.2882 0.4328

0.65ml 0.2758 0.44520.70ml 0.2658 0.4552

0.75ml 0.267 0.454

Table 6 Effect of 1M KOH at 0.70ml, 1% Indiogo

Caramine, 1.0ml of 500ppm of Potassium PeriodateSolution and 0.10ppm of Co (II).


3.0ml 0.2878 0.4478

3.5ml 0.2785 0.4571

4.0ml 0.2725 0.46314.5ml 0.2732 0.4624

Table-7 Effect of Various Ions at 0.70ml 1% Indigo-

Caramine, 4.0ml of 1M KOH, 0.1ppm of Co (II)

Ions Tolerance (ppm)

Br -,No3-, Ca(II), SO4

2- 100

Ce(III), As(V), Mog(II), Mn(II), No2- 50

Al(III), Pb(II), Mo(V), Cu(II) 10Fe(II), Fe(III) 5

Application of the Developed Method

The developed Kinetic-spectrophotometric method

was applied for the determination of cobalt (II) in

Vegetable samples like Lettuce, Endive, Cauliflower,

Cabbage and Leek. The dried sample (5.0g of each Sample)was weighed and brought into solution by dry ash methods.

The results are shown in Table-8. The results showed that

the concentration of cobalt (II) is 0.68µg highest in

Lettuce and 0.041 least in Leek. The results are comparedwith atomic absorption spectrophotometry and they are

found to be in good agreement.

Table – 8 Determination of Cobalt (II) in Vegetable

Samples

Sr. No

Name of the

Sample(5.0g of each

Sample)

Cobalt Found Recovery

% present

method

Presentmethod*

(µg)

AASmethod

(µg)

1 Lettuce 0.68 0.68 1002 Endive 0.072 0.073 98.6

3 Cauliflower 0.33 0.33 100

4 Cabbage 0.096 0.097 98.9

5 Leek 0.041 0.041 100

*Average value of three determinations

CONCLUSION

The optimum experimental conditions of the catalytic

kinetic spectrophotometric system Cobalt(II) Indigocara-

mine KOH potassium periodate were established. Under theoptimum conditions, the linear range of the determination

of cobalt(II) was 0.01-0.20 ppm and the regressionequation was y= 0.5353-2.62x, respectively. The detection

limit of the method was 0.002 ppm and Limit of Quantification is 0.007 ppm respectively. The present

method has been satisfactorily applied to the determination

of trace cobalt in Lettuce, Endive, Cauliflower Cabbage and

Leek samples.

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Kinetic-Spectrophotometric Determination of Co (II) in Vegetable Samples by Using Indigo-Caramine

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