Photometric determination of silicon in vanadium by MIBK extraction and molybdenum blue method

A photometric method for the determination of a microamount of silicon in vanadium metal is proposed. The method involves the extraction of silicomolybdic acid into methyl isobutyl ketone (MIBK) and the formation of molybdenum blue in the extract. By the method, more than 20 ppm of silicon in vanadium can be determined. The procedure is as follows. The sample is dissolved in nitric acid, evaporated to dryness, fused with sodium carbonate and dissolved with hydrochloric acid. An aliquot (V<50 mg, Si<50 μg) of the solution is taken and made up to 50 ml while keeping the acidity at 0.4M in hydrochloric acid. The solution is then treated with ammonium molybdate and oxalic acid, and silicomolybdic acid is extracted with MIBK. The extract is washed with hydrochloric acid and treated with stannous chloride solution. The absorbance is measured at 750 mμ using the solvent as a reference. The calibration curve should be prepared in the presence of the same amount of vanadium as that in sample solution.