Spectrophotometric determination of molybdenum(V) with oxine in aqueous pyridine solution

Abstract

Molybdenum(V) and oxine formed a yellowish red colored complex having 1 : 1 molar ratio soluble 40 vol% pyridine solution. At its maximum absorption, 405 nm, the molar absorptivity was 4.4 × 103. The recommended procedure was as follows.Take the sample solution containing 0.020.6 mg of molybdenum and neutralize with 6 N sulfuric acid. Add 1 ml of 6 N sulfuric acid and 4 ml of 3% hydrazinesulfate solution, and heat the solution to ca. 1 ml. The reduction of molybdenum(VI) to molybdenum(V) occurred at this stage. Cool the solution, add 2 ml of 0.6% oxine solution and 10 ml of pyridine, and dilute to 25 ml with water. Measure the absorbance at 405nm against the reagent blank. Beer's law held for 0.824 ppm of molybdenum. Interference from tungsten was removed by measuring the absorbance at 405 nmand 450 nm. Since iron and copper etc. interfered with the determination of an extent of 0.7% molybdenum ion ores, molybdenum(V) was subjected to the spectrophotometric procedure by treatment with oxine and pyridine after the separation of precipitate as α-benzoinoximate from iron and copper etc. in sulfuric acidic solution.