Comparative study of the Cd. Cu and Pb determination by AAS and by ICP-AES in river water

Comparative study of the Cd. Cu and Pb determination by AAS and by ICP-AES in river water

Water Res. Vol. 18, No. 4, pp. 423-428, 1984 Printed in Great Britain. All rights reserved 0043-1354.84 83.00 +0.00 Copyright (~ 1984 Pergamon Press ...

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Water Res. Vol. 18, No. 4, pp. 423-428, 1984 Printed in Great Britain. All rights reserved

0043-1354.84 83.00 +0.00 Copyright (~ 1984 Pergamon Press Ltd

COMPARATIVE STUDY OF THE Cd, Cu AND Pb DETERMINATION BY AAS AND BY ICP-AES IN RIVER WATER APPLICATION TO A MEDITERRANEAN RIVER ( C O N G O S T RIVER, C A T A L O N I A , SPAIN) R. RuBlo, J. HUGUET and G. RAURET Department of Analytical Chemistry, Faculty of Chemistry, Barcelona University, Barcelona 7, Spain (Received November 1982) Abstract--The accuracy, precision, detection limit and rapidity in the determination of Cd, Cu and Pb in river water by AAS determination, previous extraction with APDC-MIBK system, is compared with direct determination method ICP-AES. Both methods show a similar detection limit and an analogous accuracy by the addition standard method. With a calibration curve only ICP-AE3 presents good accuracy, this technique is advantageous in long term precision and requires minimum sample preparation. The sample stability at different temperature conservation is studied. Finally both methods are applied to the determination of Cd, Cu and Pb in Congost river water. Key words--water-analysis, trace metal analysis, river water analysis, water quality testing, cadmium, copper, lead, ICP-AES, AAS

NOMENCLATURE

room temperature and with frozen samples were studied. Both methods are applied to measure the Cd, Cu and Pb content in Congost river water at first semester of 1982. The Congost river is a 41 km long affluent of Besbs river, both are Mediterranean rivers characterized by long water mark and by irregular flow according to the rain time, they are situated in East Catalonia (Spain) (Fig. 1) between Les Franqueses and Montmel6, the Congost river crosses a highly industrialized region and the river water appears very polluted.

AAS = atomic absorption spectrometry ICP-AES = inductively coupled plasma-atomic emission spectrometry APDC-MIBK = ammonium pyrrolidine dithiocarbamatemethyl isobutyl-ketone RSD(%) = Per cent relative standard deviation. INTRODUCTION

The standard method for heavy metal determination in surface waters is based in AAS measurements with a previous extraction with A P D C - M I B K system. Several reports in ICP-AES literature (Garbarino and Taylor, 1979; Winge et al., 1977; Roura et al., 1982; Motooka, 1979) have shown that this technique is one of the best for trace element analysis in water due the great sensibility, selectivity and minimum sample preparation work. Probably in the future ICP-AES will be also recommended as standard method, so it is interesting to compare the main characteristics of both techniques. In this paper the accuracy, precision, detection limit and rapidity of the recommended standard method (APHA, 1980) is compared with ICP-AES method for Cd, Cu and Pb analysis in river water. These three metals are highly toxic upon certain concentrations and are normally present in river waters greatly polluted by industrial effluents. An important aspect in water analysis is the sample conservation, 4°C and frozen samples are recommended to minimize losses of metals (Batley and Gardner, 1977; Mart, 1979; Fukai and HuynhNgoc, 1976; Florence, 1977). In this paper stability at

EXPERIMENTAL Instrumentation

AAS. All measurements were carried out using a Perkin-Elmer Atomic Absorption Spectrophotometer (Model 4000) with double beam and background corrector. Hollow cathode lamp and air-acetylene flame is used. ICP-AES. Plasma emission spectrometry was carded out using a "Plasmatherm" source inductivelycoupled to a high frequency (27.12MHz) magnetic field operating up to 2.5kW; a thermoregulated monochromator in Czerny Turner configuration includes a holographic grating with 2400 grooves mm -t, the focal length is l m, wavelength range 190-700nm, dispersion 0.4mmmin-t and an electronic readout console, both "Jobin-Yoon'. The gas used as coolant and carrier was argon; the nebulizer is a concentric pneumatic one with a peristaltic pump. Reagents All stock solutions were prepared using ultrahigh purity metals or metal salts, APDC from Fluka, double deionized water, and high purity acids and solvents from Merck are used.

423

R. RLmo et aL

424

Les F r a n c l u e s e s /

) Gronolle

S~0~o~ ~

7

Parers

tmel6 Moiler

Montorn6s n)Oolle)

Masnou Monfcodo

)ona

~i!.

Mediterroneon

Sea

Sonf Adrio

Borcelono

L

5krn

I

Fig. 1. Map of the Congost river.

Preparation of standards Standard solutions were prepared daily from a stock solutions of Cd(ll) (1000 mg I -t ) Cu(II) 928.4 mg 1-~ ) and Pb(ll) (I 130.4mgl-~). All stock solutions were stored in polyethylene bottles. Preparation of synthetic water samples In order to study the effect of the most frequent ions in natural waters, three different synthetic water samples were prepared. Their composition is given in Table 1. Sampling Samples were taken by hand with polyethylene bottles. Prior to use all bottles were precleaned with 10% HNO 3, rinsed with double distilled water and with the sample before filling (Laxen and Harrison, 1981; Montiel et aL, 1981). For each sampling point three portions taken across the river at surface level and three at mid-depth level (20 cm of the surface level) were mixed and transferred directly to bottles. To prevent adsorption-desorption in sediments they were immediately filtered with a 0.45stm fiber-glass filter and acidified with HNOj to pH about 2. Storage time before analysis was less than 24 h. In Fig. 2 a more detailed map of a sampling points are given. Procedures AAS. The procedure described in Standard Methods (APHA, 1980) is followed, the ratio organic phase

(MIBK)-aqueous phase being maintained 1: 10. The wavelengths used were 228.8 nm for Cd; 324.7 nm for Cu and 283.3 nm for Pb. In each case the instrumental conditions were optimized. Six reference solutions were used for calibration. The blank solutions contained 100 ml double distilled water acidified with HNO 3 to pH about 2, filtered through a 0.45/am fiber-glass filter and equilibrated with l0 ml of organic phase. The same blank filtered through 3 fiber-glass filters did not give any signal by AAS for the three metals studied. ICP-AES. The "compromise conditions" used for the elements studied were the following: operating power 1.12 kW, plasma and coolant argon 201min -j, solution uptake rate 0.351rain -s, observation heigth 18 mm above the coil, integration time 15 s. The wavelengths used were Table I. Composition of the three synthetic water samples

Metal Ca2. Mg 2÷ Na*

Fe~÷ HCO~" S042CI-

A

5 I 5

0.02 II 4 I0

B

80 15 40 0.1 IOO 60 140

C

200 40 280 0.5 500 160 500

Concentration values expressed as mg I-~.

Cd, Cu, Pb by AAS and [CP-AES in Congost fiver

425

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l

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Fig. 2. Situation of the sampling points: I--Les Franqueses; 2--Granollers (entrance); 3---Granollers (city center); 4---GranoIlers-Montmel6; 5---Montmelr, before the union with Mogent fiver. 214.438 nm for Cd, 324.754 nm for Cu and 220.353 nm for Pb 0Ninge et al., 1979; Roura, 1981). Six reference solutions were used to calibrate the system. Approximately 1 min 15 s was required per analysis. The stability of analytical system was monitored by analysis of reference solution every fifth samples. The background intensity, measured after a wavelength displacement of 0.05 nm, was substrated from each measurement. The value of net signal can then be introduced in the calibration curve made with double deionized water, as the stray light effect of Ca and Mg is avoided, as a blank double distilled water acidified with HNO3 to pH about 2 filtered through a 0.45/~m fiber-glass filter was used.

RESULTS AND DISCUSSION

Spectral interferences Previously a qualitative d.c. arc spectrographic emission analysis was carried out on a dry residue of filtered sample, Ca, Mg Na, K, Sr, Si, Mn, Cr, Ag, Cu, A1, Ti and B were found present. According to Mermet and Trassy (1981) only spectral interferences of Ca, Mg, Na and Fe are of interest, so they were studied by nebulizing 1 g I-t solution of these metals and recording the spectra around the 2=,~ of the elements. Only "stray light" effect, caused by the presence of Ca(II) and Mg(II) was observed for Pb and Cd.

Conservation and stability of sample Sixteen identical samples (Cd: 2.75ngml -I, Cu 120ngml -t and Pb 33.4ngmi -t in synthetic water sampes type B) were prepared and stored in polyethylene bottles precleaned with 10% HNO3 after addition of HNO3 to pH about 2. Eight samples were frozen ( - 1 I°C) and the other eight were maintained at room temperature (17 + 3°C). A sample stored at 1 I°C and another one stored at room temperature, were analyzed weekly by AAS; the results obtained are given in Table 2. In the lowest line of this table the concentration variability after eight weeks is

given, expressed as per cent with respect to initial concentration. The results obtained showed that for no speciation measurements the conservation temperature has little influence at these concentrations.

Detection limits These were determined analogously for both techniques from 50 readings of the blank (see Procedure) and determining the S value. The expression XSL = "~'h+ 3Sh was used and the results are summarized in Table 3.

Precision Short-term precision was evaluated from two readings of each one of ten samples of identical composition obtained in an interval of 30 min. Long-term precision was evaluated from three repeated measures of the short-term precision obtained during consecutive days. The results are summarized in Table 4. In general, the ICP-AES technique gave the best long-term precision.

Accuracy A known addition recovery experiment was performed on three synthetic water samples. Known quantities of Cd, Pb and Cu were added to a synthetic water sample so the final spiked concentrations were approximately double, triple and four times the initial concentration. In ICP-AES technique two sets of experiments were performed, in one of them the initial concentration was about 100 XsL as recommended by the International Committee for the Research of Detection Limits in ICP-AES (1979), in the other experiment the initial concentration of metals were as the same order as the river samples measured. The results are given in Table 5. In AAS technique the initial concentrations of metals were chosen so that the absorption measures

426

R. Rt,'BtO et al. Table 2. Sample stability at two constant temperatures

Cd

Initial concentration After 1 week After 2 weeks After 3 weeks After 4 weeks After 5 weeks After 6 weeks After 7 weeks After 8 weeks % after 8 weeks

Pb

Cu

Room temp.

- 11 C

Room temp

- 11 C

Room temp.

- 11C

2,75 2.62 2.25 2.25 2.25 2.06 2.25 2.06 2.06

2.75 2.81 2.43 2.25 2.25 2.25 2,06 2.06 1.87

120 116 I15 108 111 108 107 108 108

120 120 ll9 114 114 109 108 109 109

36.4 36.4 32.3 32.3 32.3 28.3 28.3 28.3 24.3

36.4 36.4 32.3 32,3 28.3 28.3 28.3 24.3 24.3

74.91

68.00

66.63

66.63

89.83

90,75

Concentration values expressed as ,ug 1-~.

Table 3. Values of the detection limits for Cd, Cu and Pb calculated by ICP-AES and by AAS MIBK phase, expressed as #g I -L [CP-AES AAS MIBK phase AAS equivalence in aqueous Phase by extraction

Cd

Cu

Pb

1.7 3.7

1.7 8.2

7.5 113

0.37

0.82

11.3

of the solutions were in the lineal interval of response. The results are given in Table 6. The recovery of Cd, Cu and Pb for the same solutions using a calibration curve is calculated. The results are given in Table 5 for ICP-AES and in Table 6 for AAS.

Application to Congost river surface water Samples were taken in five points along the Congost river, at monthly intervals from January to June 1982. The samples were collected and preserved as described previously. The sampling points are shown in Figs I and 2. The Pb, Cu and Cd content was determined by AAS (standard method) and by ICP-AES; the results obtained are shown in Fig. 3, represented according to the sampling situation and grouped by different months. The results show that the three metals occur in different ratios in the five points, their average occurrence is: Cu (32.3#g1-~), Pb (16.0#gl -~) and Cd (0.56,ugl-f). In spite of the fact that the flow is low

Table 4. Short- and long-term precision Metal concentration Detection limit RSD (~) short-term RSD(~) long-term

ICP-AES AAS ICP-AES AAS ICP-AES AAS

Cd

Cu

Pb

2.9 5 14.2 17.8 16.6 17.7

27.3 58 4.1 3.6 6.7 7.2

4.5 3 5.9 12.5 13.5 13.3

Table 5. Accuracy by the ICP-AES technique

Metal

Concentration (tzg I-i )

Cd

500

5

Cu

464

46.4

Pb

565

33.9

*Three replicate determinations.

Matrix

Recovery by standard addition*

Recovery by calibration curve*

A B C A B C A B C A B C A B C A B C

103.6 103.6 97.5 87.1 91.9 86.5 104.4 104.6 99.2 94.6 99.6 100.9 98.4 100.2 95.0 92.0 89.8 87.0

100.0 97.3 91.4 96.3 83.8 84.0 100.6 95.4 92,2 105,0 105,3 98.5 97.3 99.7 90.5 105.3 89.3 95.3

C d , C u , Pb b y A A S a n d I C P - A E S in C o n g o s t river

427

Table 6. Accuracy by the AAS technique

Reco~ er.', b? standard

Concentration Metal

(,ug I - ' )

Matrix

addition*

Cd

2

Cu

92.8

A B C A B

123.3 102.7 95.8 866

46.4

Pb

226.1

33.9

C

1044 112.5

A B C A B C A B C

90.5 947 94 5 96.1 102.5 105.3 86.1 94.3 94. I

Recovery by calibration curve* 30.3 24.0 17.8 658 "73.3 79.5 78.7 82.6 82.1 48.2 51.3 53.t 55.6 63.6 63.6

*Three replicate determinations.

and the area is highly industrialized, all results are below the limits allowed now by the Spanish standards on quality of surface water. It is observed that there are some higher values due to the presence of some industrial effluents. In the sampling point number 4 the metal concentration is higher than in the other points. The results obtained by the two methods can be in disagreement but they are acceptable if we consider that the values are near the detection limit and the great quantity of organic matter present, not only 60

Standard Methods).

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Pb

40

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I II

I I I II

CONCLUSIONS

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Cu

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/

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70

e~ 60 ::1, 50 40 30 2O i

Io .

0

from natural humic acids but from all kind of organic pollutants [the high organic material content can be observed by the COD values (between 50 and 340 mg I -~) measured in the sampling points]. The absorbance values in the organic phase (calculated by the AAS technique) are greatly dependent on the kind of atom bound to the metal. This can explain the fact that, in spite of the accuracy obtained by the two methods for synthetic water samples (with only inorganic matter), results for highly organic polluted river samples show some discrepancies. Another possible cause of these discrepancies can be attributed to the use of a calibration curve (as is recommended by

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÷

÷

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Cd

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Similar values for detection limits are obtained by the two techniques. For Pb, detection limits are very high, therefore for many river graphite furnace AAS or ICP-AES, previous A P D C - M I B K extraction must be used. Short-term precision is good for both techniques but ICP-AES is better. The RSD values for tongterm precision are of the same range of short-term by ICP-AES but by AAS RSD values are worst, especially for Cd; with this technique it is necessary to take the absorbance measures of samples and standards one after another. The accuracy by the standard addition method is good and similar by the two techniques, but only ICP-AES is more accurate by the calibration curve method.

Acknowledgements--The authors wish to thank M. Roura of Servicio de Espectroscopia (University of Barcelona) for her help and knowledge in ICP-AES techniques and to Professor E. Casassas for the correction of the manuscript.

÷

REFERENCES ........

o. . . . .

11111tlt111 January

~

Illi

FebruQ r y Ma rCtl

.......

~ ......

IIIIIlILIIII ADrtl

Moy

II June

Fig. 3. Diagram of the results obtained in the Congost river water. ICP-AES: values + - . . + , detection limit - - . - - ; A A S values O O , detection limit - - - .

APHA

(1980) S t a n d a r d M e t h o d s for the Examination o f W a s t e w a t e r , 15th E d i t i o n . A m e r i c a n Public

Water and

Health Association, New York. B a t l e y G . E. and Gardner D . (1977) Sampling and storage of natural waters for trace metal analysis. Water Res. 11, 745-756.

428

R. Ru~IO et al.

Florence T. M. (1977) Trace metal species in flesh waters. Water Res. 11, 681-687. Fukai R. and Huynh-Ngoc L. (1976) Copper, zinc and cadmium in coastal waters in the N.W. Mediterranean. Mar. Pollut. Bull 7, 9-13. Garbarino J, R. and Taylor H. E. (1979) An ICP-AES method for routine water quality testing. Appl. Spectrosc, 33, 220-226. International Committee for the Research of Detection Limits in ICP-AES (1979) ICP Inform. Newslett. 3, 295. Laxen D. P. H. and Harrison R. M. (1981) The physicochemical speciation of Cd, Pb. Cu. Fe and Mn in the final effluent of a sewage treatment works and its impact on speciation in the receiving river. Water Res. 15, 1053-1065. Mart L. (1979) Prevention of contamination and other accuracy risks in voltametric trace metal analysis of natural waters. Fresenius Z. Anal. Chem. 296, 350-357. Mermet J. M. and Trassy C. (1981) A spectrometric study of a 40 MHz ICP. Discussion of spectral interferences and line intensities. Spectrochim. Acta 36B, 269-292.

Montie[ A.. Carte J.. Devoucoux J. and Bousquet G. Conservation des ~chantillons. T.M.S.-L'EA U 76e Ann~, 5, 285-290. Motooka J. M.. Mosier E. L.. Sutley S. J. and Viets J. G. (1979) ICP determination ofAg, Au, Bi. Cd, Cu, Pb and Zn in geologic materials using a selective extraction technique. Preliminary investigation. Appl. Spectrosc. 33, 456--460. Roura M. (198l) Tesis Doctoral. Publicaciones de la Universidad de Barcelona. Roura M., Baucells M., Lacort G. and Rauret G. (t982) Determination of AI in river water by [CP-AES technique. Proceedings of 2nd International Congress on Analytical Techniques in Environmental Chernisto'. pp. 377-380. Pergamon Press, Oxford. Winge R. K., Peterson V. J. and Fassel V. A. (1979) ICP-AES: prominent lines. AppL Speetrosc. 33, 206-208. Winge R. F., Fassel V. A., Kniseley R. N.. Dekalb E. and Haas Jr W. J. (1977) Determination of trace elements in soft, hard and saline waters by the ICP-AES technique. Spectrochim. Acta 32B, 327-345.