176 BASSETT AND JONES : SPECTROPHOTOMETRIC DETERMINATION [AndySt, VOl. 91 Spectrophotometric Determination of 0.01 to 0.1 per cent. of Antimony in Lead BY J. BASSETT AND J. C. H. JONES (Chemistry Department, Woolwich Polytechnic, London, S.E. 18) The development of a spectrophotometric method for the determination of small amounts (0.01 to 0.1 per cent.) of antimony in lead is described. The proposed method is based on the extraction of antimony from hydro- chloric acid solution with di-isopropyl ether, followed by spectrophotometric determination with the iodide procedure. The presence of other impurity elements usually found in lead causes no significant interference. CERTAIN physical and chemical properties of lead such as the rate of oxidation,l fatigue resistance,2 and grain size3 are influenced by the presence of small amounts of antimony. It is therefore important to have a method for determining antimony (0.01 to 0-1 per cent.) in lead that is suitable for routine use in a laboratory.Many methods have been reported in which lead is separated as lead sulphate and the antimony subsequently determined, either polarographically4p5s6 or spectrophotometrically.7 These methods are not however completely satisfactory as we have confirmed in our investi- gations that an appreciable amount of antimony may be adsorbed on the lead sulphate precipitate. The object of the present investigation was to devise a more effective separation of antimony from lead, and to determine the antimony spectrophotometrically or polaro- graphically.Ward and Lakins and o t h e r ~ ~ ~ l ~ ~ ~ ~ have reported satisfactory extraction of antimony(v) from hydrochloric acid solution with di-isopropyl ether, while Van Aman and co-workers12 have drawn attention to the importance of the order in which the reagents are added. They found that, in order to obtain maximum extraction of antimony, the di-isopropyl ether should be added to the concentrated hydrochloric acid solution before diluting the solution with water. In the preliminary experimental work, the applicability of this solvent extraction procedure to the determination of antimony in lead was investigated by using polarographic and spectrophotometric techniques. The base electrolytes used in the polarographic studies were sulphuric acid solution,l3 phosphoric acid solution14 and a mixture of hydrochloric acid and potassium bromide.l5 Results were low, possibly due to loss of antimony during its extraction from the organic phase into the base electrolyte. A spectrophotometric method12 with Rhodamine B was examined, the antimony being determined directly in the organic extract. This procedure was found satisfactory when applied to hydrochloric acid solutions containing antimony only, but failed to give repro- ducible results for antimony in lead. The second spectrophotometric method examined was that described by McChesney,lG in which the antimony is converted to the yellow iodo-antimonate ion. The method was applied to the solution obtained by evaporating the organic extract with sulphuric acid. Satisfactory results were obtained.The separation of antimony by co-precipitation on ferric hydroxide and manganese dioxide was also studied in conjunction with the iodide method of McChesney. Although fairly satisfactory results were obtained, neither procedure was as rapid and convenient as the solvent extraction method. It was concluded that, of the methods studied, the most satisfactory to be adopted as a routine procedure for determining small amounts of antimony in lead, was extraction with di-isopropyl ether followed by spectrophotometric determination as the iodide. METHOD APPARATUS- A Hilger Uvispek spectrophotometer was used for all the optical-density measurements.March, 19661 OF SMALL AMOUNTS OF ANTIMONY I N LEAD 177 REAGENTS- All reagents should be of analytical-reagent grade.Hydrochloric acid, concentrated, sp.gr. 1.18. Hydrochloric acid - bromine mixture-Shake 25 ml of bromine with 2.5 litres of hydro- Ceric sulphate solution-Dissolve 0.2 g of ceric sulphate in 100 ml of 0.1 N sulphuric acid. Di-isopropyl ether. Wash solution-Shake 60 ml of hydrochloric acid with 20 ml of di-isopropyl ether and Sulphuric acid, 50 per cent. v / v , aqueous-Prepare from sulphuric acid, sp.gr. 1.84. Sulphuric acid, 5 per cent. v / v , aqueous-Prepare from 50 per cent. v/v aqueous sulphuric Potassium iodide - ascorbic acid reagent-Dissolve 56.0 g of potassium iodide and 10 g Standard antimony solution A-Dissolve 0.6688 g of antimony potassium tartrate, chloric acid. 28 ml of water. Separate the two layers and retain the aqueous layer. acid.of ascorbic acid in 500ml of water. previously dried a t 100" C, in 500 ml of water. 1 ml = 0.0005 g of Sb. 1 ml = 0.0001 g of Sb (= 0-01 per cent. on 1-g lead sample). Standard antimopzy solution 23-Dilute 20 ml of solution A to 100 ml. PROCEDURE- Dissolve the sample (1 g for 0.01 to 0.05 per cent. of antimony, or 0.50 g for 0.05 to 0.1 per cent. of antimony) in a mixture of 50 ml of concentrated hydrochloric acid and 10 ml of hydrochloric acid -bromine solution. It is essential that the solution is not boiled a t this stage but only warmed. (If the lead sample is rolled out as thin foil of thickness approxi- mately 0.0015 inch, it will dissolve in about 20 minutes.) When dissolution is complete, cool the solution, add 1 ml of ceric sulphate solution to ensure that all of the antimony is converted to the pentavalent state.Transfer the solution to a separating funnel and make up the volume to 120 ml with concentrated hydrochloric acid. Shake the solution for 1 minute. Add 40ml of di-isopropyl ether and shake the solution for a further minute before cooling. Introduce 56ml of water into the separating funnel and shake the solution for a further period of 1 minute to extract antimony(v) into the ether layer. Cool the solution and separate the two layers. Carry out a second extraction on the aqueous layer by adding 1 ml of ceric sulphate solution, 40 ml of di-isopropyl ether and shaking the solution for 1 minute. Separate the two layers. To the combined organic extracts add 5 ml of wash solution and, after shaking, separate the organic layer and place it in a 250-ml beaker.Introduce 20 ml of 5 per cent. v/v sulphuric acid and place the beaker on a steam-bath. When the organic solvent has been removed add to the solution 6.6 ml of 50 per cent. v/v sulphuric acid. Cool the solution, add to it 25 ml of the potassium iodide - ascorbic acid reagent, filter it into a 50-ml graduated flask and dilute to the mark with water. Measure the optical density of the solution after 5 minutes in a 2-cm cell against water at a wavelength of 425mp. CALIBRATION- Transfer 1-0, 2.0, 4.0, 6.0, 8-0 and 10-ml portions of standard antimony solution B into 50-ml graduated flasks. Add to each flask 8.6 ml of 50 per cent. v/v sulphuric acid, 25 ml of potassium iodide - ascorbic acid reagent and dilute to the mark with water.Mix the solutions thoroughly and measure their optical densities after 5 minutes in a 2-cm cell against water at 425 mp. Deduct the optical density of a reagent blank solution. Prepare a calibration graph. Deduct the optical density of a reagent blank solution. RE s u LTS RECOVERY OF ANTIMONY IN THE PRESENCE OF LEAD- The procedure was studied by using 1 g of high-purity lead to which was added a known volume of standard antimony solution consisting of pure antimony dissolved in concentrated hydrochloric acid. The antimony solution was added before the hydrochloric acid - bromine178 BASSETT AND JONES : SPECTROPHOTOMETRIC DETERMINATION [ A ndySt, VOl. 91 mixture, as it was found that the presence of antimony increased the rate of dissolution of the lead.Some typical results are shown in Table I. TABLE I RECOVERY OF ANTIMONY IN THE PRESENCE OF LEAD Antimony added, per cent. 0~000 0.010 0.020 0.030 0.030 0*050 0.050 0.060 0.070 0.080 0.100 0.100 Antimony found, per cent. o*ooo 0.010 0.01 i 0.030 0.030 0.050 0.050 0.057 0.066 0.Oi 1 0.089 0.086 Error, per cent. 0 0 - 15 0 0 0 0 -5 - 6 - 11 - 11 - 14 DETERMINATION OF ANTIMONY I N THE PRESENCE OF OTHER ELEMEXTS- The method was studied in the presence of various elements that normally occur with lead. The results obtained are shown in Table 11. TABLE I1 DETERMINATION OF ANTIMONY IK THE PRESENCE OF OTHER ELEMENTS Impurity added 0.050q6 Cadmium 0.0400/, Bismuth 0.0500/, Nickel 0.050% Zinc 0.050% Arsenic 0.050% Tin 0.0647& Copper 0.0500,b Iron 0-05Oq; Tellurium 0.0500,, Selenium Form of .4ntimony added, Antimony found, Error, added impurity per cent.per cent. per cent. Cadmium chloride Lead sample containing 0-040y6 of bismuth Nickel chloride Zinc chloride Lead sample containing 0.050/, of arsenic Lead sample containing 0.05'36 of tin Lead sample containing 0.0649/0 of copper Ferric chloride Tellurium dissolvcd in nitric Sclcnium dissolved in nitric acid acid 0.030 0.030 0-030 0-030 0.030 0.030 0.030 0.030 0.030 0.030 Lcad sample containing only bismuth, copper 0.030 and silver 0.03 1 0.028 0.027 0.027 0.028 0.03 Z 0.028 0-032 0.030 0.032 0.03 1 TABLE I11 REPRODUCIBILITY OF THE METHOD WITH 0-03 PER CENT. ANTIMONY ADDED TO 1-g LEAD SAMPLES Antimony found, per cent. . . 0.028 0.027 0.030 0.027 0.030 Deviation .. . . . . 0.002 0.003 0.000 0.003 0.000 0.032 0.029 0-031 0.033 0.031 0.027 0.002 0.001 0.001 0.003 0.001 0.003 Mean = 0.030. Mean deviation = 0.002. Relative mean deviation = o'oo2 loo- = 6.7 per cent. 0.030 Standard deviation = 0.002. $ 3 - 7 - 10 - 10 - 7 + 3 - 7 $ 7 0 + 7 f 3March, 19661 OF SMALL AMOUNTS OF ANTIMONY I N LEAD 179 PRECISION OF METHOD- The reproducibility of the method was investigated with l-g samples of high-purity lead, to which the equivalent of 0.030 per cent. of antimony was added as a known volume of standard antimony solution. The results are given in Table 111. DISC~JSSION The method was found satisfactory when using a l-g lead sample containing the equivalent of 0.01 to 0.05 per cent. of antimony (see Table I). At the higher concentration range, 0.05 to 0.10 per cent., the recoveries of antimony are, however, slightly low.It is therefore recommended that when determining amounts of antimony greater than 0.050 per cent. a smaller sample should be taken so that the concentration of antimony is within the limits giving quantitative recovery. It is not possible to extend the range below 0.01 per cent. of antimony by taking more than 1 g of sample, because of the difficulty in dissolving the larger amount of lead. According to McChesney,16 only bismuth, which itself gives a colour with potassium iodide, is likely to interfere in the spectrophotometric determination of antimony by the iodide method. It was found that the di-isopropyl ether extraction separated antimony from bismuth and so eliminated this interference.No serious interference was observed from other elements investigated (see Table I I). We thank Dr. A. I. Vogel, Head of the Chemistry Department of the Woolwich Poly- technic for his interest, and one of us (J.C.H. J,) wishes to thank the Directors of Associated Lead Manufacturers for enabling him to undertake the present research. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. REFERENCES Green, F. 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Chem., 1949, 21, 753. McChesney, E. W., Ind. Engng Chem., Analyt. Edn, 1946, 18, 146. London, 1950, 290. Received J u n e 15th, 1965