determination of lead in environmental and alloy...

Indian Journal of ChemistryVol. 32A, May 1993, pp. 460-462

Determination of lead in environmental andalloy samples

A D Barve & V M Shinde*Analytical Laboratory, The Institute of Science,15 Madam Cama Road, Bombay 400 032, IndiaReceived 31 July 1992; revised 5 October 1992;

accepted 31 December 1992

A sensitive and rapid method has been proposed for theextraction and determination of microgram amounts oflead assalicylate using tris-(2-ethylhexyl)phosphate as an extractant.The lead salicylate complex is quantitatively extracted byTEHP(6%) from 7.5 x 10-4 to I X 10-2 M sodium salicylate.Various experimental parameters such as mediaconcentration, TEHP concentration, effect of pH, period ofshaking, stripping agents and diverse ions have also beenstudied. The metal ion after stripping is determinedspectrophotometrically. The log-log plot has been used' toascertain probable extractable species. The method has beenapplied for the analysis of alloy and air samples.

The hazardous effects of toxic metals present in theenvironment on human health have attracted muchattention recently. Chronic exposure to lead causesnephritis and scaring and shrinking of kidney tissues,while short but intense exposure causes functionalinjury.

Tris-(2-ethylhexyl)phosphate (TEHP) has beenearlier used in our laboratory for the extraction ofuraniumtVl)', thoriurrufv)! and telluriurnrl V)", Thepresent work has shown that TEHP can also be used forthe extraction and separation of lead from associatedelements. The method being proposed here is fast andsimple and is applicable for the analysis of alloys and airsamples.

ExperimentalA Spectronic 20 D (Milton Roy & Co)

spectrophotometer and a Control Dynamics digital pHmeter were used for the absorbance and pHmeasurements respectively.

A stock solution oflead was prepared by dissolving 2 goflead nitrate in 250 ml distilled water containing 0.5 mlcone. nitric acid. The solution was standardisedcomplexometrically" and further dilutions were made asrequired.

An aqueous solution (0.1 %) of 4-(2-pyridy-lazojresorcinol (PAR) was used for the

spectrophotometric determination of lead s.Tris-(2-ethylhexyl) phosphate (TEHP) in xylene(6%,v/v) (Aldrich, b.p. 215°) was used as extractant for lead.All other reagents used were of AR grade.

Extraction procedureTo an aliquot of solution containing lead(II), an

appropriate amount of sodium salicylate was added suchthat it's cone. was 7.5 x 10-4 - 1.0 X IO-z M in a totalvolume of 25 ml. The pH of the solution was adjustedbetween 3.9 and 6.6 with ammonia solution. The solutionwas transferred to a separating funnel and equilibratedfor 25 see with 10 ml of 6% TEHP dissolved in xylene.After phase separation, the aqueous phase was discardedand lead from organic phase was stripped with three 4 mlportions of water containing I x 10- 3 M nitric acid. Thestripped lead was finally estimated spectrophoto-metrically with PAR at 520 nm-,

Results and disciMOIlVariations in pH (2.5-8.5), TEHP concentration

(2-6% with xylene as the solvent) and salicylateconcentration (2.5 x 10-4 - 1 X 10-2 M) showed thatquantitative extraction oflead (40 ug) was feasible with10 ml of6% TEHP from 7.5 x 10-4 - I X IO-z M sodiumsalicylate solution, adjusted to pH 3.9-6.6. Variation ofequilibration time from 5-50 see showed thatquantitative extraction of lead occurs in 25 sec.Prolonged shaking gave an emulsion and made phaseseparation difficult.

The nature of the extracted species was establishedusing log-log plot. A plot oflog of distribution ratio (D)versus log of TEHP concentration at fixed salicylateconcentration and fixed pH gave a slope of 1.66indicating a molar ratio of 1:2 with respect to theextractant. TEHP causes the solvation oflead salicylatecomplex and thus promot the extraction. The probableextracted species is Pb(HOC6~COOh.2TEHP.

Of the various solvents tested, such as toluene,benzene, chloroform and carbon tetrachloride, tolueneand xylene gave quantitative extraction. Extraction withother diluents such as benzene, chloroform and carbontetrachloride was 96,73.3 and 56.77% respectively. Forall further studies xylene was selected as the diluent.

Varying amounts of diverse ions were tested for theiieffect on extraction and determination of lead (40 ug) bythe proposed method. Agrl) (1500 ug), Hg(II) (1000 ug).Ni(II) (100 ug), Cu(n) (25 ug), Ba(II) (3000 ug), Ca(IJ)

(3500 ug), Cd(lI) (300 ug), Sn(lI) (100 ug), Mg(lI) (3000ug), CoOl) (60 ug), As(lII) (~OOug), AIOII) (~SO ug),Fe(lII) (2S0 ug), Bi(lII) (80 ug), Sb(III) (SOOug), In(lII)( 1500 ug), A u( III) (2000 ug), Zr( IV) (40 ug), Te(l V) (500ug), Th(IV) (ISO ug), Ce(lV) (70 ug), Cr(VI) (\SO ug),W(VI) (SO ug), U(VI) (120 ug), phosphate (30 ug),thiosulphate (200 ug), sulphate (300 ug), oxalate (1000ug), EDT-A (100 ug), tartrate (SOOug), citrate (SOOug),nitrite (I 000 ug), thiourea (3000 ug), nitrate (2500 ug) andchloride (\800 ug) were tolerated. Zinc(lI) andmanganese(lI) interfered.

Binary separation and analysis ofsynthetic mixturesSeparation oflead(lI) (40 ug) from its binary mixtures

with mercury (II) (100 ug), antimony(lII) (40 ug),copper( II) ( 150 ug) and zinc( II) (30 ug) was carried out bythe proposed method. Mercury(lI) and antimony(III)were not extracted in the orgnaic phase and remainedquantitatively in the water phase. Mercurytll) in thewater phase was determined complexometrically" whileantimony was determined spectrophotometrically by theiodide method'. After their separations, lead(lI) wasdetermined by the proposed method. Copper(I1) andzincrll) coextracted with lead, but in the presence ofcyanide (SOOug), they were masked and their extractioninto the organic phase was prevented. The aqueous phasecontaining copper and zinc was evaporated to drynessand Cu and Zn were determined using fast sulphonblackF indicator' and PANH respectively. The averagerecovery of lcadi II), mercurytl l), antimony( III),coppcrt ll) and zincrll) from binary mixtures was 99.8S,98.22, 99.48 and 99.93% respectively.

The method also permits extraction anddetermination of lead (40 ~g)from a synthetic mixturecontaining copper ( I00 ug), zinc (40 ug), nickel (I 00 ug)and tin ( I00 ug) or cobalt (40 ug), mercury (I 00 ug) andiron (40 ug). The recovery of lead was greater than99.7YYo from triplicate analysis.

Analvsis of alloys and air-horne particulatesAlloys oflead such as leaded bronze, leaded gunmetal,

Woods alloy and tin based white metal have beenanalysed by the proposed method as follows:

The alloy leaded bronze'leaded gunmetal or tin basedwhite metal. 100 mg was dissolved in 3 ml of cone. nitricacid and the solution was evaporated. Water was addedto the residue and the precipitated metastannic acid wasfiltered. The precipitate was washed first with hot dil.nitric acid and then with hot water. The filtrate wasdiluted to 2S ml. Aliquot of each sample was taken andlead in the sample determined by the proposed method.

The Woods alloy (40 mg) was dissolved as above andfiltrate diluted to 100 ml. An aliq uot of the solution was

NOTES 4f>1

Table I· -Analysis of standard alloys for extraction of Pbt l l)[TEHP] = 6% in xylene

Alloy Composition%

Lead Standard Coefficientfound deviation ofmg* variation

0/0

Leaded bronze Cu.xu.o: Sn.9.3S: 9.23 O.OOS O.OS(BCS 364)t Pb.9.2S; Ni,0.28;

Sb.O.IS: Zn.0.13;As.0.06S; P,O.OS6;Al,O.()()2; Si,0.003

Leaded Cu.X4.06; Pb.3.15; 3.14 0.010 0.32gunmetal Sn.7.27; ZnJ.47;(BCS IK3j4)t Ni,0.13; S.O.II

Woods alloy(lndalloy 158)IndiumCorporationof America

Bi,50; Pb.26.7;Sn,I.13; Cd.IO.0

10.67 0.005 0.05 _

Tin basewhite metal(BCS 178j2)t

Sn.822: CuA.58:Ni,O.17; Bi,O.II;Fe.0.024; Sb.9AS;Pb.3.18; Cd,O.14;Zn.O.04O

3.16 0.005 OOS

tBCS = British Chemical Standard*An average of triplicate determination.

taken for the extraction and determination of lead. Theresults are reproducible and are reported in Table I.

The air samples were collected in Dahisar and RabaleSuburbs in Thane district by HVS technique using filterpaper strips These strips were supplied by theMahrashtra i-ollution Control Department, KonkanBhuvan, New Bombay. Sample filter paper strips (8sq.cm. area) were digested with 10 ml ofSO% nitric acidfor about 15 min. Distilled water was added and thesolution was filtered to remove the insoluble glass wool,filter paper residue and other dust particles. The filtratewas used for the estimation of lead. Lead found in Rilbaleand Dahisar samples by the proposed method was 0.S7~tg/mland O.SI ug.rnl respectively. The results are in goodagreement with the ICP-AES analysis of the samples(0.58 and 0.S3 Fg;1111respectively).

The proposed method is simple and accurate andpermits rapid extraction, separation and determinationof lead in air samples and alloys.

AcknowledgementThe authors thank CSIR, New Delhi, for financing the

project.

402 [ND[AN J ('HEM, SEe. A, MAY 1\1\1:1

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