Determination of bismuth by flame atomic-absorption spectrophotometry after separation by adsorption of its 2-mercaptobenzothiazole complex on microcrystalline naphthalene

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Vol. 32, No.

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3, pp. 207-208, 1985

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0039-9140/85 S3.00 +O.OO Cs 1985 Pergamon Press Ltd

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DETERMINATION OF BISMUTH BY FLAME ATOMIC-ABSORPTION SPECTROPHOTOMETRY AFTER SEPARATION BY ADSORPTION OF ITS 2-MERCAPTOBENZOTHIAZOLE COMPLEX ON MICROCRYSTALLINE NAPHTHALENE Korc~l ISHIDA, BAL KRISHAN PURI and MASATADA SATAKE Faculty of Engineering, Fukui University, Fukui 910, Japan Moor CHAND MEI-IRA Chemistry Department, Universitk de Moncton, Moncton, Canada (Received 2 November 1984. Accepted 8 November 1984)

Summary-Trace amounts of bismuth have been determined by atomic-absorption spectrophotometry after adsorption of the 2-mercaptobenzothiazole complex on naphthalene. The method has been applied to the determination of bismuth in aluminium alloys.

2-Mercaptobenzothiazole forms water-insoluble complexes with various metals. The bismuth complex is not extractable into the usual organic solvents such as chloroform, benzene, nitrobenzene and methyl isobutyl ketone. Several metals have been separated by adsorption of their complexes on microcrystalline naphthalene,‘-5 and this technique can be applied to the 2-mercaptobenzothiazole of bismuth. EXPERIMENTAL Reagents

Standard bismuth solution, 20 ppm. 2-Mercaptobenzothiazole solution in ethanol, 2%. Acetic acid/ammonium acetate buffer, lM, pH 4.5. Naphthalene solution in acetone, 20%. Procedure

Pipette a volume of sample containing 2G200 pg of bismuth into an 80-ml stoppered Erlenmeyer flask and dilute with water to about 35 ml. Add 4.0 ml of 2% 2-mercaptobenzothiazole solution and 2.0 ml of buffer. Mix and let stand for a few minutes. Add 2.0 ml of 20”/, naphthalene solution and shake the mixture vigorously fi; 30 sec. Filter through a Dauer (e.a.. No. 5C. TOYORoshi Co., Japan) placed iat on aperfor&d Teflon disc (3 cm in diameter) in an ordinary filter funnel, or a sintered glass filter (porosity 2). Wash with water, then add dimethylformamide to the filter to dissolve the naphthalene and bismuth complex, and collect the solution in a lo-ml standard flask. Aspirate the solution into an air-acetylene flame and measure the absorbance at 223.1 nm, using a bismuth hollow-cathode lamp as light-source. RESULTS

AND DISCUSSION

is quantitative when l&6.0 ml of 2-mercaptobenzothiazole solution and l-5 ml of buffer are used. Formation of the complex is complete in a few minutes. For complete adsorption of the complex 0.5-4.0 ml of the naphthalene solution is enough. The adsorption is very fast. Varying the aqueous phase volume from 30 to 100 ml has no effect on the bismuth absorbance measured but the absorbance decreases with larger volumes of aqueous phase. Beer’s law is obeyed for bismuth concentrations up to 20 pgg/ml in the final dimethylformamide solution. For ten replicate determinations of 100 pg of bismuth, the relative standard deviation found was 1.1%. The concentration giving 1% absorption was 0.34 pg/ml. The mixture of complex and naphthalene is soluble in dioxan, dimethylformamide, propylene carbonate and dimethyl sulphoxide, but dimethyl-

Fig. 1. Effect of pH, Bi, 100 pg; 2% 2-mercaptobenzothiazole solution, 2.0 ml; 20% naphthalene solution, 2.0 ml; shaking time, 30 set; wavelength, 223 nm; reference, reagent blank.

The optimum pH range for the adsorption step is 2.2-6.4 (Fig. 1). Adsorption of the bismuth complex 207

208

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Table 1. Effect of diverse ions Tolerance limit

Salt KI NaCIO, KNO, CH,COONa.3H,O NaCl NH&I Sodium tartrate Na, SO, KSCN NaF Sodium citrate Na&Q KH,PO, KCN Disodium EDTA Na, CO, Thiourea Na, SO,

70 mg lg 2 g* lg 9 mg 80 mg 10 mg 80 mg lg 50 mg 1 mg 2 mg 8 mg 1 mg 8 Pg 0.1 g lg 500 mg

Tolerance limit

Ion

Wf

2w

MW$)

;fi’+’ Pb2+ Cr(V1) Hg2+ V(V) Pt(IV) Ni*+ Cd2+ Al’+ cu2+ Zn2+ Fe’+ car+ Ti(IV) Sn2+ Sb’+

10 mg 2 mg 50 Icg 2 mg* 2 mg* 1.5 mg 2 mg 500 pg 2 mg 500 pg 300 pg 150 mg 1.8 mg

1w 1.5 mg 200 pg 300 pg 200 pg 200 pg

*Maximum value tested.

Table 2. Analysis of alloys for bismuth Composition %

Sample N.K.K. No. 916 alummium alloy

N.K.K. No. 1021 aluminium alloy Sumitomo Co. M-2-l aluminium alloy Sumitomo Co. 201 l-4 aluminium alloy Aluminium alloy

Si:0.4l,Fe:0.54,Cu:0.27 Mn:O.l1,Mg:0.10,Cr:0.05 Ni:0.06,Zn:0.30,Ti:O.l0 Sn: 0.05,Pb:0.04,V:0.02 Zr:O.O5,Ga:0.03,Co:O.03 Sb:0.01,B:0.0006,Ca:0.03 Si: 5.56,Fe:0.99,Cu:2.72 Mn :0.20,Mg: 0.29,Cr: 0.03 Ni:O. 14,Zn: 1.76,Ti:0.04 Sn:0.10,Pb:0.18,V:0.007 Zr:0.01,Sb:0.01,Ca:0.004 Si:0.29,Fe:0.071,Cu:O.O042 Ti:0.14,Mn:0.025,Mg:4.90 Cr:0.23,Zn:0.040,Be:0.0013 B:0.0002 Si:0.030,Fe:0.063$~:6.58 Ti: 0.050,Mn :0.003,Ni: 0.048 Pb:0.30,Zn: 0.003

Effect

is the most measurements.

of diverse

Present method

0.03

0.026 + 0.001

0.01

0.009 + 0.001

0.022

0.022 f 0.001

0.32

0.30 * 0.01

Bismuth*, % Direct AAS

0.55 f 0.03

*Mean of five determinations.

formamide absorption

Bismuth certified value, “/,”

suitable

0.56

Adsorption at pH 3.5. 500 mg of thiourea added.

for

the

atomic-

agreement with the certified values of those obtained by direct AAS determination. REFERENCES

ions

The procedure was applied to solutions containing 100 /*g of bismuth and various amounts of other ions, adjusted to pH 1.5-1.8 to prevent precipitation of bismuth hydroxide. The results are shown in Table 1. EDTA interferes seriously. Bismuth can be determined in aluminium alloys without prior removal of other metal ions. Table 2 gives results obtained for analysis of some standards; they are in reasonable

1. M.

Satake,

Y. Matsumura and M. C. Mehra, Mikrochim. Acta, 1980 I, 455. 2. M. Satake and M. C. Mehra, Microchem. J., 1982, 27, 182. 3. M. Satake, M. C. Mehra, H. B. Singh and T. Fujinaga, Bunseki Kagaku, 1983, 32, E165.

4. L. F. Chang, M. Satake, B. K. Puri and S. P. Bag, Bull. Chem. Sot. Japan, 1983, 56, 2000.

5. T. Nagahiro, M. Satake, J. L. Lin and B. K. Puri, Analyst, 1984, 109, 163.