Indian Journal of ChemistryVol. 32A, September 1993, pp. 827-828

Spectrophotometric determination ofcopper using tetramethylthiuram disulphide

supported on naphthalene

Ashok Kumar Malik, Atamjyot, A L J Rao* & B K Puri+Department of Chemistry, Punjabi University, Patiala 147002

Received 28 December 1992; revised 22 February 1993; accepted22 March 1993

Tetramethylthiuram disulphide supported onnaphthalene provides a rapid and economical method forthe preconcentration of copper from various samples.Copper forms a complex with tetramethylthiuramdisulphide supported on naphthalene in the column at pH4.2-7.5. The method has been applied for thedetermination of copper in various alloys, syntheticsamples and environmental samples also.

Dithiocarbamates have drawn considerableattention because of their high sensitivity to metalions especially copper'. Recently we have observedthat the metal ions are quantitatively adsorbed onmicrocrystalline naphthalene in a column along withthe chelating agent+". The newly developed columnmethod is very convenient (does not involvefiltration of the metal complex-naphthalene), rapid,economical and sensitive. The retained metalcomplex in the column along with naphthalene is noteluted after washing with water but can be dissolvedout with a suitable solvent from the column and can bedetermined directly. In the present note,tetramethylthiuram disulphide (TMTD) supportedon naphthalene has been utilised for thepreconcentration of copper from a large volume ofthe aqueous phase.

ExperimentalStandard copper solution was prepared by

dissolving the required amount in distilled water, andfurther diluted as desired". Naphthalene, DMF andall other reagents, unless specified were of AR grade.Tetramethylthiuram disulphide (from WilsonLaboratories, India) was used and its purity checkedby elemental analysis and standardised.

t Deptt. of Chemistry, Indian Institute of Technology, NewDelhi.

Preparation of loaded tetramethylthiuram disulphidenaphthalene

A mixture oftetramethylthiuram disulphide (3 g),water (10 ml) and acetone (50 ml) was stirred for a fewmin and naphthalene (lOg) was then added. Theacetone solution was diluted with distilled water upto1000 ml and stirred for half an hour and allowed tostand for about 2-3 h.

An SP-20 spectrophotometer and EeIL digitalpH meter were used. A funnel-type glass tube of 60mm in length and 5 mm in diameter was used as achromatographic column. All glass;vares andcolumns were washed with a mixture of conc.sulphuric acid and cone. nitric acid (I: I) prior to use.The column was fitted with cotton wool and thenfilled with naphthalene-chelating agent material togive a height of 0.5-0.7 em.

General procedureAn aliquot of the solution containing 1.5-20 ug of

copper was taken in a 20 ml beaker and to this wasadded 2 ml of buffer solution (sodium acetate-aceticacid, pH 6.0) and the solution diluted to 5 ml withdistilled water. Before passing the copper solutionthrough the column, it was washed with 3-5 ml of thebuffer. After the sample solution was washed with asmall volume of distilled water, the metal complexalong with naphthalene was dissolved out with 5ml ofDMF. A portion of this solution was taken and itsabsorbance measured at 430 nm against the reagentblank. The molar absorptivity and relative standarddeviation for 7.5 ug of copper are 2.96 x 1041 mol-)cm-1 and 0.8% respectively.

Results and discussionThe retention of copper was studied at different pH

values. The retention % of copper in the column was'" 100% in the pH range 4.2-7.5. In the subsequentstudy, the pH was adjusted to 6.0 'with the buffer.Addition of 0.2-6.0 ml of the buffer caused novariation in the retention (%) of copper and thus 3mlof buffer was used throughout this study. It wasobserved that the flow rate did not affect the retentionof copper within this range. A flow rate of 0.5 ml/min.was recommended. The retention capacity of thereagent supported on naphthalene was determinedby the batch method. The retention capacity ofcopper is proportional to the amount oftetramethylthiuram disulphide on naphthalene. The

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828 INDIAN J CHEM, SEe. A, SEPTEMBER 1993

Table I-Determination of copper in beers, wines, human hairand fly ash

Copper" found bypresent method

(llgJrnl)

Sample Copper" found byadsorption method

(Ilg/rnl)Beer

A 5.45 5.40B 3.48 3.47C 5.25 5.26D 4.68 4.65E 6.40 6.36

WineA 3.56 3.52B 2.97 2.95C 4.56 4.60D 4.38 4.40E 2.85 2.84

Human hairA 3.48 3.47B 4.25 4.26C 4.56 4.51D 4.42 4.38E 3.35 3.45

Fly ashA 4.78 4.72B 4.76 4.78C 4.43 4.45D 4.65 4.65E 5.40 5.38

a Mean of five determinations.

maximum capacity was found to be 4.8 mg/g oftetramethylthiuram disulphide. The retention (%) ofcopper remained constant and maximal when thevolume of the aqueous phase did not exceed 500 ml,whereas it decreased gradually with the increase inaqueous phase.

The choice of solvent for the spectrophotometricdetermination of copper is very essential because themetal chelate is insoluble in many nonaqueoussolvents. It is soluble in chloroform, carbontetrachloride, ethyl acetate, butyl acetate,acetonitrile, acetone, benzene and DMF. It was

/

found from experimental results that DMF is themost suitable solvent for dissolving out the coppercomplex, as it can be dissolved in 4-5ml of solvent andthus it further increases the sensitivity of themethod.

Effect of diverse ionsDifferent metal ions and alkali metal salts were

added individually to the solutions containing 7.5 J.Lgcopper, and the general procedure was applied. It wasobserved that many of the metal salts can be toleratedupto milligram level. The following foreign ions. (inthe amounts shown in parentheses) did noj interfere:Cl-l / B -1 NO-l CH COO-l I-I SO-2,r, 3,3 , ,4,SCN-l, POi 3, citrate, thiourea (2.5 g), EDT A (0.5mg), oxalate, tartarate (10,mg), Mg(II), Mn(II),Zn(II), Fe(III), Mo(VI), Pb(II), Al (III), Bi(III),Ca(II), V(V), Pt(IV) (3 mg), Cd(II), Co(IJ), (0.5 mg),EDT A (0.5 mg). Thus the proposed method isselective and can be used for the analysis of copper invarious samples without any preliminaryseparation.

Determination of copper in human hair, beers, winesandflyash.

A weighed amount of (10 gm) of human hair and flyash and 50 ml in case of beer or wine sample was takenand dissolved in 40-50 ml of cone nitric acid and thenevaporated to dryness. The residues thus obtainedwere dissolved in distilled water, filtered and dilutedt0250 ml with water. Copper was determined by thegeneral procedure. The results are given in Table I.The results obtained are quite satisfactory.

ReferencesI De A K, Khopkar S M & Chalmers R A, Solvent extraction of

metals (Van Nostrand and Reinhold, New York) 1970.2 Nagahiro T, Uesugi K & Satake M, Analyst. III (1986) 1389.3 Satake M, Ishida K, Puri B K & Usami S, Ana/yt Chern. 58 (1986)

2502. .4 Vogel A I, A text book of quantitative inorganic analysis. 3rd Edn

(Longman, London) 1975.