Spectrophotometric determination of molybdenum(VI) with gallein and hydrogen peroxide

Abstract

A highly sensitive method has been developed for the spectrophotometric determination of molybdenum(VI) with gallein and hydrogen peroxide in a neutral aqueous solution. The calibration curve for the spectrophotometric determination was linear in the range of (0.010.2) μg molybdenum(VI)/10 ml. The sensitivity was 0.00003 μg molybdenum(VI)/cm2 for absorbance of 0.001. The recovery of molybdenum(VI) in a waste water is (97.5102.0)%. The recommended analytical procedure is as follows. A sample solution containing less than 0.2 μg of molybdenum(VI) is taken in a 10 ml measuring flask. Two ml of 1.0 % polyvinylalcohol solution, 1.0 ml of 3.0 % hydrogen peroxide solution and 0.75 ml of 1.0 × 10-3 M gallein methanol solution are added, and then the resulting solution is adjusted to pH 6.46.9 with phosphate buffer solution. The volume is made to 10.0 ml with redistilled water, and the solution is kept at 60°C for 90 min and cooled for 5 min in water. Within 15 min the difference in absorbance between, gallein-hydrogen peroxide solution and gallein-hydrogen peroxide-molybdenum(VI) solution is measured at 530 nm against water. The effect of diverse ion on the determination of molybdenum(VI) was examined. Thorium(IV), copper(II), nickel(II), iron(III) and chromium(VI) etc. interfered, but thorium(IV), nickel(II), copper(II) and zinc(II) could be masked by the addition of 0.1 M nitrilotriacetic acid solution.