ANALYST, OCTOBER 1991, VOL. 116 1081

Ion-pair Extraction and Determination of Copper([[) and Zinc(i1) in Environmental and Pharmaceutical Samples

Purnima L. Malvankar and Vijay M. Shinde" Analytical Laboratory, The Institute of Science, 15 Madam Cama Road, Bombay-400 032, India

Copper and zinc were extracted from salicylate solution into Aliquat 336 dissolved in toluene and determined in the organic phase spectrophotometrically using 1 -(Z-pyridylazo)-Z-naphthol. The determination of copper and zinc was also carried out titrimetrically or by atomic absorption spectrometry after stripping the metal ions f rom the organic phase. The method permits the determination of copper and zinc in environmental and pharmaceutical samples. The standard deviation and relative standard deviation are 0.052 pg and 0.69%, respectively, for copper and 0.041 pg and 0.60%, respectively, for zinc. Keywords: Solvent extraction; liquid ion exchanger; salicylate solution

Considerable interest has been generated recently in the problems caused by the presence of toxic metals such as copper and zinc in environmental samples which can affect human health directly or indirectly. Heavy metals such as copper and zinc are toxic to aquatic life. Chronic copper poisoning causes gastrointestinal catarrh and haemochroma- tosis. Similarly, over-exposure to zinc results in poisonous effects. Copper is associated with Fe, Ni, Al, Mn, Pb, Zn, Cr and Mo in industrially important copper-based alloys, It is present either as the desired constituent or as an impurity in nearly all metallurgical products. Both copper and zinc are present in many alloys and are also found in a number of pharmaceutical samples and in airborne particulates, causing environmental pollution. Hence the rapid separation and determination of copper and zinc is desirable.

Various extractants such as Amberlite LA-l,lJ Primene JMT,2 tribenzylamine,z di- and triethylamine ,3 di- and tribenzylamine ,3 aliphatic amines,4 Aliquat 336,5-* Alamine 336,879 bis(2-ethylhexyl phosphate),lo mesityl oxide," trioctyl- phosphine oxide,12,13 tribenzyl phosphate,14 triisooctyl- aminel5 and Alamine 3081s have been used for the extraction of copper and zinc. In addition, other solvent extraction methods have been reviewed. 16,17 These methods, however, either give incomplete extraction,3>5.13 require a long period of time for phase separation178 or strict control of pH.4,7,9,11,15 The need for a long equilibration time1J.6~10~12~14 is also one of the limitations of the reported methods.

This paper describes a method for the extraction of copper and zinc (both at trace and macro-levels) from salicylate solution into Aliquat 336 dissolved in toluene, and their subsequent spectrophotometric determination with 1-(2- pyridylazo)-2-naphthol (PAN) in the organic phase. Alter- natively, milligram amounts of copper and zinc are stripped from the organic phase and determined either titrimetrically or by atomic absorption spectrometry (AAS). The proposed method is relatively simple, rapid, free from many interfer- ences and has a wide range of applications in the analysis of pharmaceutical and environmental samples.

Experimental Apparatus and Reagents

A Bausch and Lomb Spectronic 20 spectrophotometer, a Control Dynamics digital pH meter with a combined glass electrode and a Varian Techtron AA6 atomic absorption spectrometer were used.

The stock solutions of copper and zinc were prepared by dissolving 0.98 g of copper sulphate and 1.13 g of zinc

* To whom correspondence should be addressed.

sulphate, respectively, in 250 ml of distilled water containing 0.1% sulphuric acid. The solutions were standardized by known methods. 18 The test solutions of lower concentrations were prepared by suitable dilutions.

A 5% solution of Aliquat 336 (methyltrioctylammonium chloride; Fluka) in toluene was equilibrated for 45 min with an equal volume of 2 mol dm-3 sodium salicylate solution and used as an extractant.

A 0.1% methanolic solution of PAN was used for the determination of copper and zinc.lgJ0

Extraction Procedure for Copper(I1) and Zinc(I1)

Microgram amounts of copper or zinc are extracted from a 25 ml aliquot solution using the optimum extraction conditions given in Table 1. Copper or zinc in the organic phase is determined spectrophotometrically as follows. For copper, add 9.5 ml of buffer solution of pH 2 (prepared using 0.2 rnol dm-3 potassium chloride and 0.2 rnol dm-3 hydrochloric acid solutions) and 0.5 ml of 0.1% PAN solution in methanol, then shake for 1 min, separate the organic layer and measure the absorbance of the orange complex at 560 nm against the reagent blank prepared analogously.19 For zinc, add 5 ml of acetate buffer solution of pH 5.8 (prepared using 0.1 rnol dm-3 acetic acid and 0.1 rnol dm-3 sodium acetate solutions) and 1 ml of 0.1% PAN solution in methanol, then shake for 2 min and measure the absorbance of the orange complex at 550 nm against the reagent blank which was prepared similarly.20 Calculate the copper or zinc content from the calibration graph. Milligram amounts of copper or zinc are stripped and determined either titrimetricallylg or by AAS at 324.7 nm (copper) and 213.9 nm (zinc).

Results and Discussion The optimum extraction conditions for copper and zinc were established by varying the pH (4.5-8.0), sodium salicylate concentration (0.01-0.50 rnol dm-3), Aliquat 336 concentra- tion (0.5-5% in toluene) and period of equilibration (30-180 s). The optimum extraction conditions are reported in Table 1.

Several diiuents such as xylene, benzene, hexane, carbon tetrachloride, chloroform and toluene were examined for the extraction of copper and zinc. The results showed that the quantitative extraction of copper and zinc was feasible only with toluene and xylene. Toluene was used as a diluent for further studies as it gave clear phase separation.

The log-log plots of distribution ratio versus salicylate concentration (at fixed pH and Aliquat 336 concentration) and Aliquat 336 concentration (at fixed pH and salicylate concentration) gave slopes nearly equal to 2 for both copper

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1082 ANALYST, OCTOBER 1991, VOL. 116 ~~~~ ~ ~

Table 1 Optimum extraction conditions for copper(i1) and zinc(1i)

[Salicylate]/ [Aliquat 3361 Metal ion mol dm-3 (Yo 1 PH c u (1-5 0.25-0.50 2.5 4.5-5.1

c u (500 CLg) 0.25-0.50 2.5 4.5-5.1

Zn (10-40 pg) 0.11-0.50 3.0 4.5-8 .O

Zn (500 Pg) 0.11-0.50 3.0 4.5-8.0

* Reference 19. t Reference 18. $ Reference 20.

Extraction Stripping period/s agent

- 90

90 2 x 5miof

60 1 rnol dm-3 HCI

-

60 2 x 5mlof 1 mol dm-3

ammonia solution

Determination Determined in the organic

Determined iodimetrically? layer with PAN*

Determined in the organic

Determined complexo- layer with PAN$

metrically?

Table 2 Analysis of airborne particulates

Copper found by proposed

using AAS by AAS* method" Copper found

after prior to Standard Sample extraction/ extraction/ deviation/

No. mgm-3 mgm-3 mgm-3 1 2.20 2.22 0.028 2 1.83 1.82 0.014 3 1.41 1.42 0.015 4 0.86 0.86 0.006 5 2.75 2.76 0.012

* Average of six determinations.

Relative standard deviation

1.27 0.77 1.06 0.70 0.44

(Yo)

proposed method. Copper was determined iodimetrically .I8 Similarly, 10 mg each of Ba", CrV1, Mg", Call, chloride, tartrate, ascorbate, thiocyanate, phosphate, chloride, iodide, bromide, thiourea, sulphate, nitrate, nitrite, cyanide, tung- state, vanadate and thiosulphate; 5 mg each of Ag* and O s v ~ ~ ~ ; 2.5 mg each of A1111 and molybdate; 1.2 mg each of oxalate and citrate; and 0.5 mg each of Pb", Mn", Bi"' and Pd" do not interfere with the extraction and determination of zinc using the proposed method. Zinc was determined complexometric- alIy.18 However, Pb", Fe"' and oxalate interfere with the extraction of copper, whereas Fe111, Ni", Curl and ethylene- diaminetetraacetic acid interfere with the extraction of zinc and must be absent.

Table 3 Analysis of industrial waste-water samples

Zinc found by proposed method*

using AAS Relative after Zinc found Standard standard

Sample extraction by AAS* deviation deviation

1 0.22 0.23 0.002 0.91 2 0.18 0.18 0.001 0.56

No. ( P P 4 (PPm) (PPm) (%)

* Average of six determinations.

and zinc, indicating a metal to salicylate and metal to Aliquat 336 ratio of 1 : 2 in the extracted species. It can therefore be concluded that the extracted species is probably [ (R4N)t2M(HOC6H4COO)22-] involving an anion-exchange extraction process between the metal salicylate and the amine salt in the organic phase.

Various stripping agents of different concentrations were examined for the back-extraction of the metal ion from the organic phase. The quantitative stripping of copper was possible with two 5 ml portions of HCI (1-3 rnol dm-3), H2S04 (1-3 rnol dm-3), ammonia solution (1-2 rnol dm-3) and three 10 ml portions of water, whereas the stripping of zinc was possible with two 5 ml portions of HCI (1-4 rnol dm-3), H2S04 (1-4 rnol dm-3), H N 0 3 (1-4 rnol dm-3), NaOH (1-2 rnol dm-3) and ammonia solution (1-2 rnol dm-3).

Various cations and anions were added to a fixed amount of copper and zinc (0.500 mg of each) in order to study the effect of interferents on the extraction and determination of these two metals using the proposed method. The tolerance limit was set at the amount required to cause an error of +2% in the recovery of the metal. The results showed that 10 mg each of Ba", AllL1, Zn", Mg", CrV1, Hg", Mn", Ca", Sn", Pd", chloride, bromide, phosphate, nitrate, tartrate, fluoride, ascorbate, thiocyanate and sulphate; 5 mg each of iodide, tungstate and thiourea; and 2.5 mg of Au"' do not interfere with the extraction and determination of copper using the

Applications

Analysis of environmental samples The proposed method was applied to the separation and determination of zinc in an industrial waste water sample collected from the Maharashtra Pollution Control Board, Central Laboratory, New Bombay. The method was also applied to the analysis of airborne particulates collected by the Municipal Corporation, Air Quality Monitoring, Bombay. The particulate samples were brought into solution by digesting the samples with 20% HN03; after filtration, the solution was diluted to 100 ml with distilled water. An aliquot (20 ml) of the solution was taken for the extraction and determination of copper using the proposed method. The results are presented in Tables 2 and 3.

Analysis of pharmaceutical samples The proposed method was also applied to the separation and determination of copper and zinc in a number of pharmaceutical samples such as Supradyn, Theragran-M, Fersolate, Vimgran, Zevit, Shield ointment and Nycil powder. Iron was found to co-extract with copper when extracted with a 5% solution of Aliquat 336 in toluene from 0.50 rnol dm-3 salicylate solution adjusted to pH 4.7; however, copper was first stripped with water and determined titrimetrically. 18 Iron was subsequently stripped with two 5 ml portions of 1 rnol dm-3 HCI and determined spectrophotometrically.21 Zinc was separated from iron and copper by extraction from 0.50 rnol dm-3 sodium salicylate solution adjusted to pH 8. Both copper and iron remained in the aqueous phase. Zinc was stripped from the Aliquat 336 phase with two 5 ml portions of 1 rnol dm-3 ammonia solution and determined using the proposed method.18 Ten tablets or the contents of ten capsules were powdered and ignited. The ash was dissolved in 2 ml of concentrated HCI, filtered and the solution diluted to 100 ml. Shield ointment (0.628 g) and Nycil powder (0.350 g) were taken up in solution in the same manner. An aliquot (5.5, 2.5, 7.5, 5.0, 0.5, 2.0 and 1.0 ml, respectively) of solutions of the pharmaceuticals listed above

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ANALYST, OCTOBER 1991, VOL. 116 1083

Table 4 Determination of copper andor zinc in pharmaceutical samples (IP = Indian Pharmacopoeia; USP = United States Pharmacopeia)

Sample Supradyn

(Roche)

Theragran-M (Sarabhai Chemicals)

Vimgran (Sarabhai Chemicals)

Fersolate (Glaxo)

Composition

Copper sulphate IP, 3.39 mg; zinc sulphate IP, 2.20 mg; sodium borate IP, 0.88 mg

Potassium iodide IP, 0.2 mg; dried iron(i1) sulphate IP, 41 mg; copper sulphate IP, 8 mg

Calcium carbonate USP, 250 mg; iron(i1) sulphate IP, 34 mg; potassium iodide IP, 0.2 mg; potassium sulphate, 1.0 mg; copper sulphate IP. 4 mg; manganese sulphate, 6.6 mg; magnesium oxide, 10.0 mg

Dried iron(ii) sulphate IP, 195 mg; copper sulphate IP (1966), 2.6 mg; manganese sulphate, 2.6 mg

* Average of six determinations. 1- mg per tablet. $ mg per capsule.

Relative standard

Certified CdZn Standard deviation value found* deviation

Cu, 0.861- Cu, 0.851- 0.012-t 1.41

Zn, 0.50-t Zn, 0.491- 0.0081- 1.60

Cu, 2.001- Cu, 1.99t 0.0141- 0.70

Cu, l.00-t Cu, 0.97-t 0.0131-

Cu, 0.661 Cu, 0.64$ 0.0121

1.54

1.88

Tabie 5 Determination of zinc in pharmaceutical samples (IP = Indian Pharmacopoeia; BP = British Pharmacopoeia; USP = United States Pharmacopeia)

Relative standard

Certified Zn Standard deviation Sample Composition value found* deviation (%)

Zevit (SKF) ZnS04.7H20, 61.8 mg; Zn, 22.501- Zn, 22.401- 0.21-t 0.94 thiamine monohydrate IP, 10 mg; riboflavine IP, 10 mg; nicotinamide IP, 75 mg; pyridoxine hydrochloride IP, 2 mg; cyanocobalamine IP, 7.5 pg; calcium pantothenate, 25 mg; tocopheryl acetate IP, 20 mg; ascorbic acid IP, 150 mg

Nycil (Glindia) Chlorphenesin BP, 1%; boric acid IP, 5% ; zinc oxide IP, 16%; starch IP, 51% ; talc purified IP to 100%

Zn, 12.80$ Zn, 12.71$ 0,151

Shield ointment (SKF) Lidocaine USP, 3% Zn, 3.93§ Zn, 3.904 0.034

m/m; hydrocortisone acetate IP, 0.25% m/m; zinc oxide IP, 5% m/m; allantoin, 0.5% m/m; ointment base q.s.

* Average of six determinations. t mg per capsule. $ mg per 100 mg of powder. § mg per 100 mg of ointment.

1.17

0.71

was taken for the extraction and determination of copper and zinc using the proposed method. The results are presented in Table 4 and 5.

determination of metal ions. The method is relatively fast and permits the extraction and determination of both copper and zinc in real samples, namely pharmaceutical and environmen- tal samples. The method is accurate and precise.

Conclusion Solvent extraction is the simplest and least expensive of all the separation techniques. The proposed method permits the extraction, separation and simultaneous spectrophotometric

References 1 De. A. K., Ray, U. S., and Parthi, N. J., J . Indian Chern. Soc.,

1982, 59, 1334.

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15 McDonald, C. W., and Earhart, B. P., Sep. Sci. Technol., 1979, 14,741.

16 Sekine, T., and Hasegawa, Y., Solvent Extraction Chemistry. Fundamentals and Applications, Marcel Dekker, New York, 1977.

17 De, A. K., Khopkar, S. M., and Chalrners, R. A., Solvent Extraction of Metals, Van Nostrand Reinhold, New York, 1970.

18 Vogel, A. I., A Text-Book of Quantitative Inorganic Analysis, Longman, London, 3rd edn., 1961, pp. 349,358,432 and 443.

19 Betteridge, D., John, D., and Snape, F., Analyst, 1973,98,512. 20 Bhanu, R., and Shinde, V. M., Talanta, 1989,36,469. 21 Marczenko, Z., Spectrophotometric Determination of Elements,

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Paper 1 t02033A Received April 30th, 1991 Accepted June 19th, 1991

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