Analyst, August, 1974, Vol. 99, @. 469470 469 A Modification to the Extraction = Atomic- absorption Method for the Determination of Antimony, Bismuth, Lead and Tin BY K. THORNTON (Henry Wiggin and Co. Ltd., Holmer Road, Hereford) AND KEITH E. BURKE (The International Nickel Company, Inc., Paul D. Merica Research Laboratory, Sterling Forest, Suffern, New York 10901, U.S.A.) It has been shown that the use of organometallic compounds for the calibration procedure used in the extraction - atomic-absorption determination of antimony, bismuth, lead and tin in metallurgical materials leads to erroneous results at low concentration levels. Results are presented, which demonstrate that the technique is satisfactory when calibrated with solutions that have been taken through the extraction procedure, THE previously published analytical method for the determination of trace amounts of antimony, bismuth, lead and tin1 depends on the extraction of the iodides of these elements into a solution of tri-n-octylphosphine oxide (TOPO) in 4-methylpentan-2-one.The extract is then nebulised directly into the atomic-absorption flame. The calibration procedure involves the use of solutions of organometallic compounds in 4-methylpentan-2-one. It is shown in Table V of the original publication1 that agreement between this procedure and two other atomic-absorption techniques is generally acceptable at higher concentration levels of the elements determined. Furthermore, the accuracy is shown to be satisfactory at these higher levels for the analysis of standardised samples (Table VI of the original publication).At lower concentration levels, particularly below 10 p.p.m., the agreement between the three techniques is poor and it is difficult to assess the accuracy of the extraction procedure as no certified standards are available at these levels. Subsequent work has shown that the calibration procedure that makes use of organo- metallic compounds dissolved in 4-methylpentan-%one gives rise to erroneous results, the values being, in general, higher than the true values. However, a simple modification, in which aqueous solutions of the elements determined are carried through the extraction pro- cedure and treated in the same way as the sample solutions, overcomes this difficulty. This modification avoids any error that might be introduced by variation in the extraction con- ditions or errors due to light scattering, molecular absorption or organometallic bonding.The revised procedure has been applied to several of the samples included in Table VI of the original publication. Originally, two alternative atomic-absorption techniques were used for comparison purposes. The comparison procedure with a simple 4-methylpentan-2-one extraction is subject to the same problems that have been encountered with the proposed method, with TOPO in solution in 4-methylpentan-2-one, whereas the separation technique based on co-precipitation with manganese dioxide is inherently less sensitive and consequently inaccurate at levels below about 10 p.p.m. In an effort to overcome these difficulties alter- native analytical procedures have been developed that involve solvent-extraction separations followed by square-wave polarographic determination.Lead was extracted as the iodide complex in a method similar to that proposed by Luke,3 and bismuth, tin and antimony were extracted as their complexes with isoocty1thiog1ycollate.* The results obtained by using the modified extraction - atomic-absorption procedure and the polarographic methods are given in Table I. @ SAC and the authors.470 THORNTON AND BURKE TABLE I DETERMINATION OF ANTIMONY, BISMUTH, LEAD AND TIN IN COMMERCIALLY AVAILABLE MATERIALS Found, p.p.m. A r 3 Designation HW E-3923 HW E-3924 HW E-3925 HW E-3926 HW E-3927 HW E-3928 HW E-3929 HW E-3930 HW E-3931 HW E-3932 HW B-7047 HW B-7048 HW B-7049 HW B-7050 HW B-7051 BCS 310 BCS 310/1 BCS 387 BCS 371 NBS 671 NBS 672 HW F-292 HW F-293 HW F-294 HW F-295 HW F-296 HW F-297 Matrix TINCOLOY alloy 800 INCOLOY alloy 800 INCOLOY alloy 800 INCOLOY alloy 800 INCOLOY alloy 800 INCOLOY alloy DS INCOLOY alloy DS INCOLOY alloy DS INCOLOY alloy DS INCOLOY alloy DS TINCONEL alloy X750 INCONEL alloy X750 INCONEL alloy X750 INCONEL alloy X750 INCONEL alloy X750 TNIMONIC alloy 90 NIMONIC alloy 90 NIMONIC alloy 901 Commercial nickel Nickel oxide Nickel oxide Nickel Nickel Nickel Nickel Nickel Nickel Antimony 4+ A* 6 13 11 12 13 12 9 7 9 9 1 <1 <1 <1 <1 4 4 3 1 <l <1 2 <1 <1 <1 <1 <1 B* 4 13 12 12 13 12 11 9 10 11 1 1 1 1 1 5 5 1 <1 <1 <1 <1 (1 <1 <1 - - Bismuth - A B <0.5 <Om5 <Om5 <0*5 (0.5 <0*5 <0.5 <0.5 <0*5 <0*5 <Om5 <0.5 <0.5 <0.5 <O-5 <0*5 (0-5 ( 0 .5 t 0 . 5 <0.5 <0.5 <0*5 <0*5 <0*5 <0*5 <0*5 <0.5 ( 0 . 5 <0.5 <Om5 (0.5 ( 0 . 5 (0.5 <0*5 <O-5 <0*5 <On5 (0.5 (0.5 <0.5 (0.5 <0*5 <O-5 <On5 <Om5 <0*5 <0*5 <0*5 <0*5 (0.5 ( 0 . 5 (0.5 (0.5 - Lead 4+ A 1.0 1.2 1.0 0.8 1.0 0.9 1.0 1.0 1.0 1.0 1.5 1.2 1.2 1.3 1-3 5.7 0.5 15 14 14 35 0.8 0.8 1.4 0.9 1.1 0.3 B 1.7 1.2 1.8 1.4 1.4 1.4 0.9 0.9 1.1 1.1 1-5 1.3 1-2 1.6 1-3 5.5 0.7 15 - 16 39 0.8 0.8 1.7 0.5 1.0 0-5 Tin + A 17 20 23 24 20 20 19 19 13 19 7 7 3 3 3 21 35 19 <1 <2 <2 <1 <1 <1 <1 <1 <1 B 25 24 24 23 21 22 17 20 19 19 6 6 6 4 4 24 34 18 3 4 3 <1 <1 <1 <1 <1 - * Laboratory A used the modified TOP0 - atomic-absorption procedure, while laboratory B used t INCOLOY, INCONEL and NIMONIC are registered trademarks of The International Nickel solvent extraction - polarographic methods. Company, Inc. REFERENCES 1. 2. 3. 4. Burke, K. E., AnaZyst, 1972, 97, 19. Leonard, M. A., and Swindall, W. J., Ibid., 1973, 98, 133. Luke, C. L., Analytica Chim. Acta., 1967, 39, 447. Fritz, J. S., Gillette, R. K., and Mishmash, H. E., Analyt. Chem., 1966, 38, 1869. Received July 2nd, 1973 Accepted February 20th, 1974