Coordenao de Anlises Minerais COAM Setor de Caracterizao Tecnolgica - SCT

SIMULTANEOUS SPECIATION OF

CHROMIUM BY SPECYTOPHOTOMETRY AND MULTICOMPONENT ANALYSIS

Maria Ins Couto Monteiro Manuel Castro Carneiro

Arnaldo Alcover Neto Ricardo Soares

Srgio de Souza Henrique Junior Fernanda Veronesi Marinho Pontes

Llian Irene Dias da Silva Ricardo Erthal Santelli

Setembro/2009

CT2009-034-00 Comunicao Tcnica publicada na revista Chemical Speciation and Bioavailability, pg.153-160-2009.

Simultaneous speciation of chromium by

spectrophotometry and multicomponent analysis

Ricardo Soaresa, Manuel Castro Carneiroa, Maria Ines Couto Monteiroa*,Sergio de Souza Henrique Juniora, Fernanda Veronesi Marinho Pontesa,Llian Irene Dias da Silvaa, Arnaldo Alcover Netoa and Ricardo Erthal Santellib

aSetor de Caracterizacao Qumica, COAM, Centro de Tecnologia Mineral, Av. Pedro Calmon, 900,

Ilha da Cidade Universitaria, Rio de Janeiro - RJ, 21941-908, BrazilbDepartamento de Geoqumica, Universidade Federal Fluminense, NiteroIyRJ, Brazil*E-mail: mmonteiro@cetem.gov.br

ABSTRACT

A simple, fast and sensitive spectrophotometric method for the simultaneous determination of Cr(III)and Cr(VI) in effluents and contaminated waters using a UV-visible spectrophotometer, which operateswith an advanced software for multicomponent analysis, is proposed. The method consists in thecomplexation of Cr (III) with EDTA and reaction of Cr(VI) with diphenylcarbazide (DPC). Variables, suchas pH and colour stability time, were studied. The effect of concomitant ions on the simultaneous Cr(III)and Cr(VI) determination was also investigated. The sums of the chromium species concentrationsobtained by the proposed method were compared with the total chromium concentrations found byelectrothermal atomic absorption spectrometry. Recoveries of the chromium species between 75 and136% were obtained for spiked samples. The linear working range for Cr(III) was 0.530mg L 1, whilefor Cr(VI) was 0.0050.30mg L 1. The detection limits were 0.3mg L1 for Cr(III) and 0.003mg L 1 forCr(VI) while the quantification limits were 1.0mg L 1 for Cr(III) and 0.01mg L 1 for Cr(VI).

Keywords: chromium speciation, multicomponent analysis, spectrophotometry, tannery effluent,contaminated water

INTRODUCTION

Chromium is used in several industries such as

metallurgical (steel, ferrous- and nonferrous alloys),

refractory (chrome and chrome-magnesite) and

chemical engineering (pigments, dyes, electroplating,

tanning, cooling water, leather and wood preservation

and cement manufacturing). As a consequence of

these industrial activities, chromium compounds

enter the environment causing pollution (Han et al.,

2007; Hagendorfer et al., 2008).

The two main oxidation states of chromium, Cr(III)

and Cr(VI), present in natural waters, significantly

differ in biological, geochemical and toxicological

properties. Over a narrow concentration range, triva-

lent chromium is considered essential for mammals

for the maintenance of glucose, lipid and protein

metabolism, whereas Cr(VI) is reported to have a

toxic effect on humans (Lin et al., 2001; Monteiro

et al., 2002).The high toxicity of Cr(VI) is related to

its ability to cross the cell membrane and its strong

oxidation properties (Girard et al., 1996). Hexavalent

chromium is readily soluble in water and can be

accumulated in soil and plants (Kumar et al., 1997),

while Cr(III) probably exists in environmental waters

in the form of many different species: hydrolysed,

complexed and adsorbed on colloidal matter. Also,

Cr(III) can undergo speciation changes from inor-

ganic form to organic complex by plants, being

transported as carboxylate complex (Juneva and

Prakash, 2008). Fortunately, not all of the chromium

released by industrial plants is Cr(VI). In many cases,

waste solutions are subjected to reduction, releasing

Cr(III) to the environment (Pankow et al., 1974).

Chemical Speciation and Bioavailability (2009), 21(3) 153

www.scilet.com

doi: 10.3184/095422909X466095

However, in natural environmental compartments

like soil and water, the interconversion of Cr

species takes place readily, depending on pH, redox

potential and ligands available (Kumar et al., 1996).

In Great Britain, the allowable concentration of

chromium is limited to 15 mg L 1 for surface waters(Chwastowska et al., 2005). The Brazilian environ-

mental legislation (CONAMA, 2008) states that

Cr(III) and Cr(VI) in final effluents should not

exceed 1.0mg L 1 and 0.1mg L 1, respectively.There are several methods for the determination of

Cr(III) and Cr(VI) in aqueous solutions. One option

consists in the complexation and selective extraction

of both Cr(III) and Cr(VI) before instrumental

analysis, which involves laborious and time-

consuming steps. Another alternative is to determine

Cr(VI) and total chromium, after Cr(III) oxidation,

and then calculate the Cr(III) concentration by

subtraction (Gomez et al., 2006). However, the

conversion of metal species from one form to

another can cause serious problems including incom-

plete conversions (particularly at low concentrations),

introduction of contamination by the oxida-

tionyreduction agents and interferences from othermetals. In addition, these procedures are generally

time-consuming (Sperling et al., 1992).

One of the most used colorimetric methods for the

Cr(VI) andyor total chromium determination isbased on the reaction of Cr(VI) with diphenylcarba-

zide (DPC) (Lynch et al., 1984; Andrade et al.,

1985; Milacic et al., 1992; Sule et al., 1996;

Clesceri et al., 2002; Mulaudzi et al., 2002; Giusti

et al., 2005). The absorbance of the redviolet

complex of unknown composition, formed at the

pH range of 1.62.2, is read at 540 nm (Clesceri

et al., 2002). Chromium (III) does not react with the

DPC reagent (Pflaum et al., 1956). The sample

acidification carried out before the DPC addition

prevents the solubilization of Cr(III) species, the

releasing of Cr(III) from complexes or colloidal

particles, or even the increase of Cr(VI) reduction

by organic compounds in the sample (Sule et al.,

1996). Studies showed that interferences from orga-

nically complexed Cr(III) species were almost negli-

gible in soil extracts when non-acidified DPC was

used, and more significant with acidified DPC

(Milacic et al., 1992). Elemental interference

studies revealed that concentrations as high as

200mg L 1 Mo or Hg could be tolerated.Vanadium concentrations up to 10 times higher

than Cr concentrations did not cause any trouble.

Iron concentrations greater than 1mg L 1 produced

a yellow colour, but the Fe(III) colour was not

strong and no interference was found. Alternative

procedures such as the use of chloroform to remove

interfering amounts of Mo, V, Fe and Cu by the

extraction of the metals cupferrates (Clesceri et al.,

1998), as well as the removal of organic compounds

from the samples (Mulaudzi et al., 2002), have been

proposed.

Very few methods for Cr determination are based

on the formation of Cr(III) complexes in aqueous

solution, and this is probably due to the slow

reaction rate of the strongly hydrated Cr(III) ions.

Even so, methods based on the formation of an

extremely stable complex of Cr(III) with ethylene-

diamintetraacetic acid (EDTA) have been used (Den

Boef et al., 1960; Costa et al., 1999; Gomez et al.,

2006). Optimum pH values for the Cr(III)-EDTA

complex formation were lower than 5 (from 2.5 to

4.0 or pH 4.75) (Costa et al., 1999; Gomez et al.,

2006), since the Cr(III) solubility decreases at pH

values higher than approximately 5 (Sule et al.,

1996; Fendorf, 1995). Studies revealed that

Cr :EDTA molar ratios from 1 : 3 to 1 : 18 couldbe used (Costa et al., 1999). Reaction times of 5min

at 90C, using a heating plate (Gomez et al., 2006),and of 3min with microwave oven irradiation

(92C) (Costa et al., 1999) have been reported.The complex was stable for at least 30 days

(Gomez et al., 2006). The wavelengths for the

maximum absorbance of Cr(III)-EDTA complex

were 540 nm (Gomez et al., 2006), 542 nm (Costa

et al., 1999) and 545 nm (Den Boef et al., 1960).

Interference studies showed that 2 g L 1 of Al, Ba,Bi, Cd, Ca, Pb, Sr, La, Mn, Hg, Mo, W, Ti, U, V

and Zn, as well as 0.5 g L 1 of Cu, Co, Ni and Fe,did not cause any interference on 0.1 g L 1 Cr(III)absorbance signal (Costa et al., 1999). The alkaline

and alkaline earth metals and the more common

anions, such as Cl , NO3 , CH3COO

andSO4

2 , did not interfere on the Cr(III)-EDTAabsorbance signal (Den Boef et al., 1960).

Simultaneous spectrophotometric determination of

several components is a very complex problem in

analytical chemistry due to spectral interferences,

which results in widely overlapped absorption

bands. In these cases, the conventional univariate

calibration method is impracticable due to contribu-

tion of one species on the absorption signals of

others and vice versa. Then, other methods have

been used, such as multicomponent analysis

program. It is based on an extension of Beers law

to various components. The multicomponent cali-

154 Simultaneous speciation of chromium by spectrophotometry and multicomponent analysis

bration uses the analytical function concept of

combining absorbance and derivative data to give

function results. This technique usually improves

the resolution bands, eliminates the influence of

background or matrix and provides more defined

fingerprints than traditional ordinary or direct absor-

bance spectra, since it enhances the detectability of

minor spectral features. Derivative transformation

permits discrimination against broad band interfer-

ents, arising from turbidity or non-specific matrix

absorption, and it tends to emphasize subtle spectra

features, allowing the enhancement of the sensitivity

and specificity in mixtures analysis (Rojas and

Ojeda, 2009).

The multivariate curve resolution method has been

recently used for chromium speciation in tanning and

environmental samples (Gomez et al., 2006). In a

first step, Cr(III) was determined as the Cr(III)

EDTA complex, while in a second step, Cr(VI) was

determined by the addition of a NaOH solution that

converted the dichromate to chromate, in the

presence of the Cr(III) EDTA complex. Limits of

detection of 8mg L 1 for Cr(III) and 2mg L 1 forCr(VI) were obtained. Methods for simultaneous

spectrophotometric determinations of Cr(III) and

Cr(VI) have not been found.

This paper describes a simple, fast and sensitive

spectrophotometric method for the simultaneous

determination of Cr(III) and Cr(VI) in effluents

and contaminated waters with the aid of a UV-vis

spectrophotometer equipped with a computer with

advanced software for multicomponent analysis.

EXPERIMENTAL

Equipment

The chromium concentration measurements were

performed on a spectroscopy system based on an

Agilent 8453 spectrophotometer and an Agilent

ChemStation advanced software for multicomponent

analysis (MCA) on a Hewlett-Packard 7540

computer (Waldbronn, Germany). The system was

equipped with an automatic pumping sampler model

1FS. The chromium species spectra were recorded

from 300 to 900 nm. The data analysis parameters for

spectral processing were: first-order derivative, filter

length of 5; polynomial degree of 4; wavelength

range of 450680 nm; reference wavelength range

of 820850 nm and maximum likelihood calculation

method. A continuous flow quartz cuvette with a

1 cm optical path and 62mL was used. The pumping

and washing times were 30 and 15 s, respectively.

The solution heating was performed on a heating

plate from Mistura Equipamentos para Laboratorio

model MA 085 (Piracicaba, SP, Brazil). All pH

measurements were carried out with a pH meter

with a combined glass electrode from Thermo

Electron Corporation, model Orion (Beverly, MA,

USA). The samples preliminary analyses were carried

out by using an inductively coupled plasma optical

emission spectrometer (ICP-OES) from Horiba Jobin

Yvon, model Ultima 2 (Longjumeau, France) and a

modular ion chromatograph (IC) from Metrohm

(Herisau, Switzerland). The determination of total

chromium was performed on an electrothermal

atomic absorption spectrometer (ET AAS) Varian

model AA-240 Z (Victoria, Australia) equipped

with Zeeman-effect background corrector. All

measurements were made at 357.9 nm, by using a

Cr hollow-cathode lamp (Varian) with a current of

6mA and a bandwidth of 0.2 nm. The temperature

program was the same employed by Monteiro et al.

(2002) for atomization on a pyrolytic graphite plat-

form. The analyte addition method was used.

Reagents, standards and samples

All solutions were prepared with analytical grade

reagents and ultra-pure water, obtained from a

Milli-Q water purification system (Millipore Corp.,

Millford, MA, USA). All glassware vessels were

soaked in 12% (vyv) HNO3 for 24 h and rinsedthoroughly with distilled water and, finally, rinsed

for the last time with ultra-pure water.

Standard stock solutions containing 1000mg L 1

Cr (III) and 1000mg L 1 Cr (VI), as CrCl3 andK2CrO4, were prepared from Titrisol concentrate

(Merck, Darmstadt, Germany) and Fixanal concen-

trate (Riedel-de-Haen, Seelze, Germany), respec-

tively. Intermediate low concentration solutions of

Cr(III) and Cr(VI) were prepared daily by dilution of

the corresponding stock solution with water. Sulfuric

acid, EDTA, DPC and acetone were supplied from

Vetec Qumica Fina Ltda (RJ, Brazil). A 0.45mol

L 1 sulfuric acid solution was prepared. A DPCsolution was prepared by dissolving 250mg of the

reagent in 50mL of acetone. In the interference

study, NaCl, Na2SO4 (both from Vetec Qumica

Fina Ltda, RJ, Brazil) and NaNO3 (from Merck,

Darmstadt, Germany) were used to prepare the

stock solutions of 1000mg L 1 Cl , SO42 and

NO3 . Also, standard stock monoelemental solu-

tions containing 1000mg L 1 of Al, Mn, Fe, Ni,

Maria Ines Couto Monteiro et al. 155

Zn and Cu were used. These solutions were prepared

from AlCl3, Mn(NO3)2 (Merck, Darmstadt,

Germany), Fe(NO3)3, Ni(NO3)2, Zn(NO3)2 and

Cu(NO3)2 (VHG Labs, Manchester, NH, USA).

Three tanning and beamhouse effluent samples

from the same tannery, collected at time intervals of

5min, and one water sample from Paraibuna River,

collected close to the tannery and other industrial

areas, were analysed. The certified reference mate-

rials SRM 1643d trace elements in water, SRM

1640 trace elements in natural water, both from

NIST, USA and SLRS-3riverine water, from

National Research Council Canada, containing

18.53+ 0.20mg L 1, 38.6+ 1.6 mg kg 1

(density 1.0015 g cm 3 at 22C) and0.30+ 0.04mg L 1 of total chromium, respectively,were analysed and also used for recovery experi-

ments.

Procedure

A sample aliquot, previously filtered on a 0.45mmmembrane, containing about 0.0252.5mg of Cr(III)

and 2.515 mg of Cr(VI) was transferred to a 125mLErlenmeyer flask. In this work, aliquots of 25mL

were taken from the samples. Only the tanning and

beamhouse effluents were previously diluted 10 and

50 times, respectively. Then, an excess of EDTA

(65mg) was added for Cr(III) complexation. A

0.45mol L 1 sulfuric acid solution (about 500mL)was added until pH 4.5. The solution was heated at

90C for 5min. A cold finger condenser containing

cold water was used to avoid evaporation. After

cooling at room temperature, 1mL of DPC solution

(5mg) was added to react with Cr(VI). The solution

was transferred to a 50mL volumetric flask, and the

volume was completed with purified water. The

solution was let stand for 510min for full colour

development. Then, it was pumped to the 62mLcuvette for spectrophotometric analysis. Blank and

mixed standard solutions had the same treatment. The

mixed standard solutions used in the analytical work

were: 0.005mg L 1 Cr(VI)y0.5mg L 1 Cr(III),0.01mg L 1 Cr(VI)y1.0mg L 1 Cr(III), 0.05mgL 1 Cr(VI)y5.0mg L 1 Cr(III), 0.10mg L 1

Cr(VI)y10mg L 1 Cr(III), 0.20mg L 1

Cr(VI)y20mg L 1 Cr(III) and 0.30mg L 1

Cr(VI)y30mg L 1 Cr(III).

RESULTS AND DISCUSSION

Influence of the pH on the absorbance signals of

Cr(III) and Cr(VI)

The effect of pH (2.5, 3.5 and 4.5) on the absorbance

signals of 50mg L 1 Cr(III) and 0.05mg L 1

Cr(VI) solutions was investigated. The experiment

was performed in triplicate. The highest absorbance

signals for Cr(III) and Cr(VI) at 544 nm were

obtained at pH 4.5 and, therefore, it was selected.

The Cr(III)-EDTA and Cr(VI)-DPC spectra produced

by the analyses of 50mg L 1 Cr(III) and 0.05mgL 1 Cr(VI) solutions, in the wavelength range of 300to 900 nm, are depicted in Figure 1.

156 Simultaneous speciation of chromium by spectrophotometry and multicomponent analysis

Figure. 1 Cr(III) EDTA and Cr(VI) DPC spectra produced by 50mg L 1 Cr(III) and 0.05mg L 1 Cr(VI) in the wavelength range of300 to 900 nm. (22) Cr(III) EDTA and (- - -) Cr(VI)DPC.

Stability study

Mixed standard solutions containing 0.003mg L 1

Cr(III)y0.3mg L 1 Cr(VI), 0.005mg L 1 Cr(III)y0.5mg L 1 Cr(VI), 0.05mg L 1 Cr(III)y5.0mgL 1 Cr(VI) and 0.30mg L 1 Cr(III)y30mg L 1

Cr(VI) were analysed by the proposed procedure.

The chromium species concentrations were measured

at the elapsed times of 0 (after 510min for the

colour development), 1, 2, 3, 12, 24 and 40 h. The

glass flasks containing the coloured solutions were

covered with aluminium foil to avoid exposure to

light, and the flasks used for the times 12, 24 and 40 h

were also kept in a refrigerator, and brought up to

room temperature before beginning the proposed

procedure. The experiment was carried out in tripli-

cate. Negative concentrations were found for the

mixed standard solutions containing 0.003mg L 1

Cr(III)y0.3mg L 1 Cr(VI) at elapsed time zero andtherefore, they were eliminated. The relative standard

deviations of the chromium species concentrations

for the remainder mixed standard solutions were

lower than 8%. The average recoveries of the chro-

mium species in these solutions at different elapsed

times are present in Figure 2. The recoveries at time

zero have been put to 100%. All the solutions

remained stable up to at least 24 h, when the

Students t-test at 95% of confidence level was

used for comparison of the average concentrations

with those obtained at time zero. Also, good agree-

ment was obtained between the found and theoretical

chromium species concentrations up to 24 h, when

regression lines were applied. Slopes from 1.0049 to

1.0784 and from 0.9811 to 1.1058; intercepts from

0.2701 to 0.4897 and from 0.00001 to 0.0049;

productmoment correlation coefficients from

0.9987 to 0.9998 and from 0.9993 to 0.9998 were

obtained for Cr(III) and Cr(VI), respectively. These

results indicate good linearity in the ranges of 0.005

0.30mg L 1 for Cr(VI) and 0.530mg L 1 forCr(III) up to 24 h.

Interference study

The sample preliminary results obtained by ICP-OES

and IC and the sample final dilution factors for the

proposed method were used to select the ion concen-

tration ranges for the interference study on the

determination of the chromium species. A solution

containing 20mg L 1 Cr(III) and 0.2mg L 1 Cr(VI)was used (Table 1). The experiment was carried out

in triplicate. Tolerance limits of interfering ions were

Maria Ines Couto Monteiro et al. 157

Figure 2 Average recoveries of chromium species at different elapsed times (n 3).

established at those concentrations that did not cause

recoveries lower than 90% and higher than 115%.

The results indicated that Cu2 (from 0.1 to 0.2mgL 1), Ni2 (0.2mg L 1) and SO4

2 (from 1000 to3000mg L 1) caused slightly higher Cr(III) recov-eries (from 120 to 122%). Interferences of the

potential coexisting ions on the Cr(VI) recoveries

were not observed.

Analytical results

The detection limit (LOD) was defined as three times

the standard deviation (3s) of three consecutive

measurements of the lowest concentration, and the

quantification limit (LOQ) was defined as 10s,

considering in both cases the two-fold dilution of

the sample in the analytical procedure. The LODs

were 0.3mg L 1 for Cr(III) and 0.003mg L 1forCr(VI). The LOQs were 1.0mg L 1 for Cr(III) and0.01mg L 1 for Cr(VI). The relative standard devia-tions were lower than 11%. The LOQs meet the

limits of the Brazilian regulation of 1.0mg L 1 forCr(III) and 0.1mg L 1 for Cr(VI) in final effluents(CONAMA, 2008).

Table 2 shows the results for the chromium

species in spiked samples. The experiment was

carried out in triplicate, and all relative standard

deviations were lower than 17%. The initial concen-

trations of Cr(III) and Cr(VI) in the certified water

samples SLRS-3, NIST 1640 and NIST 1643b were

not detected by the proposed method, which can be

explained only for SLRS-3: total chromium

(0.30+ 0.04mg L 1) was lower than the LOQs ofchromium species found by the proposed method.

For NIST 1643b, the non detection of Cr(VI) is in

agreement with the result obtained by Sperling et al.

(1992), who attributed this fact to a probable result

of the sample conservation used by NIST.

According to the certificate, the sample was

conserved in 0.5mol L 1 nitric acid. In this condi-tion, Cr(III) is the predominant species (Brookins,

1988). Chromium species recoveries between 75

and 136% were obtained for the spiked samples.

Table 3 shows the sums of the concentrations of

chromium species determined by the proposed

method and the total chromium concentrations

obtained by the ET AAS method. The chromium

species sums for the tanning effluents B and C and

the beamhouse effluent A were in good agreement

with the total chromium concentrations obtained by

the comparative method, when the Students t-test,

at 95% confidence level was applied (n 3). The

158 Simultaneous speciation of chromium by spectrophotometry and multicomponent analysis

Table 1 Effect of potential coexisting ions on the simultaneousdetermination of 20mg L 1 Cr(III) and 0.2mg L 1 Cr(VI)(n 3)Ion Concentration Recovery (%)

(mg L 1)Cr(VI) Cr(III)

Al3 0.1 97+ 1 102+ 80.5 97+ 1 98+ 20.7 94+ 4 102+ 11.0 98+ 4 101+ 25.0 99+ 4 100+ 110 99+ 6 103+ 2

Cu2 0.005 103+ 5 99+ 10.01 96+ 3 106+ 50.02 102+ 6 103+ 30.05 90+ 4 115+ 20.1 94+ 5 121+ 40.2 100+ 14 120+ 3

Fe3 0.5 96+ 5 102+ 21.0 98+ 10 103+ 23.0 100+ 5 98+ 25.0 90+ 3 99+ 110 94+ 7 101+ 430 101+ 6 104+ 12

Mn2 0.05 94+ 5 104+ 10.1 95+ 6 102+ 30.2 96+ 9 99+ 10.5 90+ 7 102+ 11.0 90+ 3 94+ 105.0 98+ 11 99+ 4

Ni2 0.001 94+ 3 104+ 20.02 96+ 10 106+ 30.01 90+ 2 113+ 10.05 102+ 3 104+ 10.1 91+ 3 113+ 10.2 93+ 1 121+ 1

Zn2 0.05 95+ 3 106+ 40.1 95+ 4 103+ 20.2 96+ 4 100+ 60.5 100+ 7 107+ 21.0 98+ 3 107+ 12.0 92+ 5 113+ 5

Cl 10 93+ 8 93+ 450 95+ 4 101+ 2100 100+ 9 110+ 1250 90+ 5 98+ 31000 107+ 4 113+ 72500 90+ 17 113+ 9

NO3 0.2 103+ 10 97+ 3

1.0 102+ 16 108+ 21.5 105+ 9 110+ 52.0 94+ 7 110+ 710 100+ 7 109+ 415 83+ 3 110+ 6

SO42 50 95+ 4 103+ 7

100 94+ 10 96+ 2300 93+ 11 96+ 3500 100+ 12 102+ 221000 90+ 5 121+ 33000 98+ 4 122+ 8

results obtained for the tanning effluent sample A

and beamhouse effluents B and C were slightly

lower (913%) but acceptable, when the regression

line was applied for all effluent samples

(slope 0.8751; intercept 9.984; productmoment correlation coefficient 0.9997).

CONCLUSIONS

The proposed method for Cr(III) and Cr(VI) simulta-

neous spectrophotometric determination in effluents

and contaminated waters is simple and fast. The

linear working range for Cr(VI) was 0.005

0.30mg L 1, while for Cr(III) was 0.530mg

L 1. The detection limits were 0.3mg L 1 forCr(III) and 0.003mg L 1 for Cr(VI) while thequantification limits were 1.0mg L 1 for Cr(III)and 0.01mg L 1 for Cr(VI). Better limits could beobtained by using lower dilution factor of the sample

in the analytical procedure.

ACKNOWLEDGEMENTS

The authors thank the Conselho Nacional de

Pesquisas e Desenvolvimento Tecnologico (CNPq)

for financial support. We also thank Amanda

Gerhardt de Oliveira and Fernanda Nunes Ferreira

for the analytical support.

Maria Ines Couto Monteiro et al. 159

Table 2 Analytical results of Cr(III) and Cr(VI) in spiked samples (n 3)Sample Chromium concentration (mg L 1)

Cr(III) Cr(VI) Cr(III) Cr(VI) Cr(III) Cr(VI)initial initial added added found found

Water SLRS-3 ND ND 5.0 0.05 5.2+ 0.1 0.052+ 0.00110 0.10 9.80+ 0.01 0.097+ 0.00120 0.20 20.2+ 0.2 0.203+ 0.00230 0.30 30.3+ 0.3 0,302+ 0.003

Water NIST 1640 ND ND 10 0.10 12.1+ 0.2 0.14+ 0.0230 0.30 27.3+ 0.5 0.300+ 0.00650 0.50 44.0+ 0.2 0.485+ 0.005

Water NIST 1643d ND ND 10 0.10 9.20+ 0.02 0.089+ 0.00230 0.30 29.7+ 0.4 0.276+ 0.00350 0.50 51+ 1 0.460+ 0.005

Water from the ND ND 5.0 0.05 5.9+ 0.1 0.0445+ 0.0005Paraibuna River 10 0.10 12+ 2 0.117+ 0.014

20 0.20 27+ 2 0.186+ 0.00730 0.30 35+ 5 0.279+ 0.008

Tanning effluent 143+ 1 1.2+ 0.1 5.0 0.05 148.6+ 0.2 1.26+ 0.0510 0.10 153.7+ 0.1 1.38+ 0.0220 0.20 169+ 1 1.40+ 0.02

Beamhouse 764+ 10 6.7+ 1.0 5.0 0.05 769.9+ 0.3 6.8+ 0.1effluent 10 0.10 774.0+ 0.3 6.9+ 0.3

20 0.20 783+ 1 6.9+ 0.230 0.30 796+ 2 7.1+ 0.1

ND, Not detected.

Table 3 Comparison of the total chromium concentrations (mg L 1) obtained by theproposed and ET AAS methods (n 3)Sample Proposed method ET AAS method

Tanning effluent A 139+ 4 152+ 2Tanning effluent B 137+ 2 140+ 3Tanning effluent C 141+ 34 151+ 4Beamhouse effluent A 752+ 23 836+ 23Beamhouse effluent B 734+ 11 823+ 17Beamhouse effluent C 748+ 19 859+ 26

REFERENCES

Andrade, J.C., Rocha, J.C. and Baccan, N. (1985) Sequential

spectrophotometric determination of Cr(III) and Cr(VI)

using flow injection analysis. Analyst, 110, 197200.

Brookins, D.G. (1998) Eh-pH diagrams for geochemistry.

Springer-Verlag, New York.

Chwastowska, J., Skwara, W., Sterlinska, E. and Pszonicki, L.

(2005) Speciation of chromium in mineral waters and salinas

by solid-phase extraction and graphite furnace atomic

absorption spectrometry. Talanta, 66, 13451349.

Clesceri, L.S., Greenberg, A.E. and Eaton, A.D. (1998) Standard

methods for the examination of water and wastewater, 20th

edn. American Public Health Association, Washington, USA.

Costa, A.C.S., Assis, J.C.R., Torres, A.L.C., Ferreira, S.L.C.,

Korn M.G.A. and Gomes, L.S. (1999) Uso de irradiacao de

microondas na determinacao espectrofotometrica de cromo

com EDTA. Qum. Nova, 22, 194196.

Den Boef, G., De Jong, W.J., Krijn, G.C. and Poppe, H. (1960)

Spectrophotometric determination of chromium(III) with

EDTA. Anal. Chim. Acta, 23, 557564.

CONAMA (Environmental National Council of Brazil) (2008)

Standards for domestic water supply, resolution number 397;

CONAMA: Braslia, DF.

Fendorf, S.E. (1995) Surface reactions of chromium in soils and

waters. Geoderma, 67, 5571.

Girard, L. and Hupert, J. (1996) Speciation of chromium(VI) and

total chromium determination in welding dust samples by

flow-injection analysis coupled to atomic absorption spectro-

metry. Talanta, 43, 19651974.

Giusti, L. and Barakat, S. (2005) The monitoring of Cr(III) and

Cr(VI) in natural water and synthetic solutions: an assess-

ment of the performance of the DGT and DPC methods.

Water, Air, Soil Pollut., 161, 313334.

Gomez, V., Larrechi, M.S. and Callao, M.P. (2006) Chromium

speciation using sequential injection analysis and multivari-

ate curve resolution. Anal. Chim. Acta, 571, 129135.

Hagendorfer, H. and Goessler, W. (2008) Separation of chromiu-

m(III) and chromium(VI) by ion chromatography and an

inductively coupled plasma mass spectrometer as element-

selective detector. Talanta, 76, 656661.

Han, Z., Qi, L., Shen, G., Liu, W. and Chen, Y. (2007)

Determination of chromium(VI) by surface plasmon field-

enhanced resonance light scattering. Anal. Chem., 79, 5862

5868.

Juneva, S. and Prakash, S. (2008) Electrophoretic study of

chromium speciation in xylem sap of maize (Wintr Crop).

Chem. Spec. Bioavail., 20(2), 5563.

Kumar, S.J., Ostapczuk, P. and Emons, H. (1997) Determination

of total chromium in terrestrial and marine samples by

electrothermal atomic absorption spectrometry after pressure

digestion. Fresenius J. Anal. Chem., 359, 171175.

Lin, T.W. and Huang, S.D. (2001) Direct and simultaneous

determination of copper, chromium, aluminum, and manga-

nese in urine with a multielement graphite furnace atomic

absorption spectrometer. Anal. Chem., 73, 43194325.

Lynch, T.P., Kernoghan, N.J. and Wilson, J.N. (1984) Speciation

of metals in solution by flow injection analysis. Part 1.

Sequential spectrophotometric and atomic-absorption detec-

tors. Analyst, 109, 839842.

Milacic, R., Stupar, J., Kozuh, N. and Korosin, J. (1992) Critical

evaluation of three analytical techniques for the determina-

tion of chromium(VI) in soil extracts. Analyst, 117, 125

130.

Monteiro, M.I.C., Avila, A.K. and Neumann, R. (2001) Deter-

mination of chromium by electrothermal atomic absorption

spectrometry in waters using a forked platform and co-

injection of Mg as chemical modifier. Anal. Chim. Acta,

428, 265278.

Monteiro, M.I.C., Fraga, I.C.S., Yallouz, A.V., Oliveira, N.M.M.

and Ribeiro, S.H. (2002) Determination of total chromium

traces in tannery effluents by electrothermal atomic absorp-

tion spectrometry, flame atomic absorption spectrometry and

UV-visible spectrophotometric methods. Talanta, 58, 629

633.

Mulaudzi, L.V., van Staden, J.F. and Stefan, R.I. (2002) Deter-

mination of chromium(III) and chromium(VI) by use of a

spectrophotometric sequential injection system. Anal. Chim.

Acta, 467, 5160.

Pankow, J.F. and Janauer, G.E. (1974) Analysis for chromium

traces in natural waters: preconcentration of chromate from

ppb levels in aqueous solutions by ion exchange. Anal.

Chim. Acta, 69, 97104.

Pflaum, R.T. and Howick, L.C. (1956) The chromium-diphenyl-

carbazide reaction. J. Am. Chem. Soc., 78, 48624866.

Rojas, F.S. and Ojeda, C.B. (2009) Recent development in

derivative ultravioletyvisible absorption spectrophotometry:20042008 A review. Anal. Chim. Acta, 635, 2244.

Sperling, M., Xu, S. and Welz, B. (1992) Determination of Cr(III)

and Cr(VI) in water using flow injection on-line preconcen-

tration with selective adsorption on activated alumina and

flame atomic absorption spectrometric detection. Anal.

Chem., 64, 31013108.

Sule, P.A. and Ingle, J.D. Jr. (1996) Determination of the specia-

tion of chromium with an automated two-column ion-

exchange system. Anal. Chim. Acta, 326, 8593.

160 Simultaneous speciation of chromium by spectrophotometry and multicomponent analysis

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