Catalytic spectrophotometric determination of trace molybdenum in natural- and tap-water samples.

A sensitive and simple catalytic spectrophotometric method for the determination of molybdenum has been developed using the molybdenum-catalyzed oxidation of L-ascorbic acid with hydrogen peroxide in the presence of ο-phenylenediamine to produce quinoxaline derivatives. The absorbance of the solution was measured at 340 nm for the determination of molybdenum after reacting for 5 min at pH 3.2 and 25°C and readjusting the pH of the solution to 1 with hydrochloric acid to stop the reaction. The calibration graph was, linear up to 4 ng/ml of molybdenum. The detection limit was 0.03 ng/ml (0.2 ng). The proposed method was successfully applied to river-, rain- and tap-water samples.