Indian Journal of ChemistryVol. 25A. January 1986. pp. 99-100

Atomic Absorption SpectrophotometricDetermination of Coppertl): Extraction

as 3-(2-Pyridyl)-5, 6-diphenyl-l, 2, 4-triazine Tetraphenylborate TernaryComplex into Molten Naphthalene

T NAGAHIRO. M SATAKE & B K PURl*t

Faculty of Engineering, Fukui University. Fukui 910, Japan

Received 29 June 1984; 'rerised and accepted 13 May 1985

A sensitive atomic absorption spectrophotometric method hasbeen developed for the determination of copper after extraction of its3-{2-pyridyl)-5, 6-diphenyl-l, 2, 4-triazine tetraphenylborate ternarycomplex into molten naphthalene in the pH range of 1.5-8.5. Beer'slaw is obeyed in the concentration range of7-90 Jig of copper in 10 mlof DMF solution. Ten replicate determinations of a samplecontaining 40 Jig of copper give a mean absorbance of 0.260 with arelative standard deviation of 1.2%. The sensitivity for I~o

absorbance is 0.068 Jlg/ml. The method has been applied to thedetermination of copper in alloys and human hair.

3-{2-Pyridyl)-5,6-diphenyl-l,2A-triazine (PDT) formsa coloured, water-insoluble, thermally stable ternarycomplex with copper (I) in the presence oftetraphenylborate (TPB) anion t -3. This complex isnon-extractable into common organic solvents due topoor solubility, but can be easily extracted into moltennaphthalene. The advantages of using moltennaphthalene over the usual liquid-liquid extractionhave already been outlined in some previouspapers" -8. Extraction of this complex into moltennaphthalene has been made use of in developing amethod for the determination of copper in variousalloys and biological samples by atomic absorptionspectrophotometry.

Solution of copper nitrate was prepared in distilledwater and standardized by known methods". Solutionof PDT (0.05'1;,) was prepared in ethanol. while thesolutions of TPB (1 'YJ and hydroxylammoniumchloride(2~;';) were prepared in water. A buffer solutionof pH = 5.0 was prepared by mixing acetic acid (I M)and ammonium acetate (I M) solution. A Perkin-Elmermodel 403 atomic absorption spectrophotometerfitted with a copper hollow cathode lamp and a Toa-Darnpa, HM-5A pH meter was used.

Procedure for determination of coppen.I)To an aliquot of copper solution (7-90 Jig) were

added solutions of hydroxylammonium chloride

+Departmcnt of Chemistry. Indian Institute of Technology. HauzKhas. New Delhi 110016

(l ml), PDT (2 ml), buffer (2 ml), I 'X, TPB (2 ml) andenough ammonium acetate solution to give a 0.1 Mconcentration after dilution to the required volume (~ 30 ml). This solution was mixed well and warmed ona water-bath at 60°(' for 5 min. Naphthalene (0.7 g)was added to it and the temperature raised to 85-90' Cto melt naphthalene completely. and shakenthoroughly till naphthalene separated out as a solidmass. The solid mass was filtered off. dissolved inDMF. the volume madeupto 10ml with DMF and thesolution aspirated into air-acetylene name at 324.7 nmusing a copper cathode lamp.

React-en conditions were established by tak ing40 Jig of copper. The extraction was found to bequantitative if the concentration of the electrolyte(sodium acetate, sodium chloride or potassium nitrate)was >0.05 M, indicating the salting out effect. TheCu(I)-PDT -TPB complex was quantitatively extractedinto molten naphthalene (0.3 to 0.7 g) in the pH range1.5-8.5. Addition of 1-5 ml of the acetate buffer (pH5.0) had no effect on the extraction.

It was found that coppertll) was completely reducedto copperrl) with 0.25-5.0ml of 2°,;, solution of thereducing agent. The extraction was quantitative for1.0-5.0 ml of 0.05% PDT and 0.3-3.5 ml of 10

." TPBsolutions. Hence to provide a safety margin. 1.0 ml ofthe reducing agent. 2.0 ml of PDT and TPB solutionswere used throughout the present study.

A minimum standing time of 5 min at 60c(' is

recommended. though the reaction is complete in lessthan 2 min. The extraction is very rapid. beingpractically complete in less than 5 see and a shakingtime of Imin is considered safe enough. The extractionis quantitative if the aqueous phase volume is keptbetween 25 and 45 ml.

The metal complex and naphthalene mixture isfound to be insoluble in many of the common organicsolvents but was soluble III DMF dimethylsulphoxide, propylene carbonate or acetonitrile. 0 M Fhas been selected since the absorbance is maximum inthis solvent.

Beer's law was obeyed over the concentration range7.90 jig of copper in 10 ml of the DMF solution. Tenreplicate determinations of a sample containing 40 Jigof copper gave a mean absorbance of 0.26. relativestandard deviation 1.2"" and sensitivity O.O(-,~ Jig mlfor I"" absorbance. The present method is moresensitive than the direct atomic absorption spectre-photometry.

99

INDIAN J. CHEM., VOL. 25A, JANUARY 1986

Table I-Analysis of Copper in Various Alloy Samples.

Alloy Composition Copper (%)(%)

Present+ Found

NBS Ni:0.084, Mg:I.49 3.99 4.08 ±0.08SRM-85-b, Mn:0.61, Cr:0.21aluminium Si:0.18, Fe:0.24alloy Zn:0.03, Ti:0.0022

Pb:0.02l. Ga:0.019V:0.006,

NBS, Mn:0.014, Ni:O.OO6 1.01 1.015 ±0.007SRM-94c Sn:0.006, AI:4.13Die casting Cd:0.OO2, Fe:0.018alloy Pb:0.OO6, Mg:0.042

NBS,SRM-627zinc-basealloy

0.138 ±0.OO5AI:3.88,Fe:0.023,Cd:0.OO5LCr:0.OO38,Ni:0.OO29.

Mg:0.030 0.132Pb:0.0082Sn:0.0042

Mn:0.014Si:0.021

NBS,SRM-171,magnesium-

basealloy

Si:0.01l8 0.0112 0.0114 ±0.OOO3AI:2.98Fe:0.OOI8

Mn:0.45.Ni:O.OOO9.Pb:0.OO33,

Zn:1.05,

*Mean of 5 individual determinations.+Certified value.

Interference studiesSample solutions containing 40,lg of copper and

various amounts of diverse ions were prepared andanalysed by this' procedure. The following (in theamount shown in parentheses) did not interfere: K Br,NaI, NaCl04, KN03, CH3COONa.3H20, NaCI,NH4C1, Na2S04, NaF, KSCN, KH2P04 (2 g each);Na1C204 and KCN (0.1 mg each); sodium tartrate andsodium citrate (1.5 mg each) and disodium EDTA(1.0/lg) (only EDTA interfered seriously. Theextraction was almost nil when the amount of EDT Awas > 60 JIg probably due to the formation of acomplex, the formation constant of which was higherthan that of PDT-TPB complex): Cd2+ (1500 rng),Mg2+ (600 mg), Ca2+ (50 mg); Zn2+ and AI3+ (30 mgeach; in case of A13+ the extraction was carried out atpH =4.0); Mn2+ (20 mg); Pb2+. Ru3+ and Rh3+ (10

100

mg each); Pt4+ (8 mg), Cr3+ (7 mg), WO+ (6 mg): Hg2+and V5 + (4 mg each), Ni2+ (2 mg), Ag + (1.5 mg), Bi3+(1.2 rng), Co2+ (25 /lg), Fe3+ (20 Ilg) and Pd2+ (4 /lg)(Only Pd2+ interfered seriously). When the con-centrations of these ions increased beyond the limitmentioned above, percentage extraction of CU(l)started decreasing. Ions like K +, N H:eel. gave precipitate with TPB anion in the abs-ence of copper. However. only a light turbidityappeared in the presence of copper, which disappearedon heating the solution at 80-90°C during extraction.

Determination of copper in alloysAn alloy sample (0.05-0.5 g) was completely

dissolved in cone, hydrochloric acid (I: I 20-30 ml) byheating on a water-bath. To this was added H 202 (30%, v]v; 2-3 ml), excess peroxide decomposed by heating,the mixture cooled, diluted to 500 ml with distilledwater and copper determined as described in theprocedure (Table I).

Determination of copper in human hairA sample of human hair (lOg) was digested with a

mixture of cone. nitric acid (30 ml) and cone. perchloricacid (8 ml) till the final volume was 5-6 ml. Aftercooling, this solution was diluted to 200 ml with water.an aliquot of this sample taken and copper determinedas described elsewhere in this note. The amount of Cuin human hair (0.0015 ± 0.0003'/;,) found by the presentmethod was in satisfactory agreement with that(0.0018±0.0005'1;.) obtained by the DDTC-MIBKmethod 10.

ReferencesI Schilt A A, Talanta, 13 (1966) 895.2 Schilt A A & Hoyle W C. Analyt Chem, 39 (1967) 114.3 Schilt A A & Taylor P J. Analyt Chem, 42 (1970) 220.4 Puri B K & Gautam M, Talanta, 25 (1978) 484.5 Gautam M & Puri B K, Mik rochim AC/a. 1 (1979) 515.6 Wasey A, Bansal R K. Puri B K & Rao AU, Talanta, 31 (1984)

205.7 Wasey A. Bansal R K & Puri B K, M ikrochim AC/a, 1(1984) 211.8 Satake M, Nagahiro T & Puri B K, Analyst, 109 (1984) 3.1.9 Vogel A I, A textbook of' quantitatire inorganic analvsis

(Longmans, London) 1969.10 JIS. KOI02 (1981) 153.