Catalytic-spectrophotometric determination of trace amounts of molybdenum(VI) ion

A new simple, sensitive and rapid catalytic kinetic method for the determin ation of trace amounts of molybdenum(VI) ion is described. The method is ba sed on the catalytic effect of Mo(VI) on reduction reaction of Nile blue A (NBA) by hydrazine dihydrochloride (HD) in acidic media. The reaction was m onitored spectrophotometrically by measuring the decrease in absorbance of the reaction mixture at 634 nm. The fixed time method was used for the firs t 3 min from initiation of the reaction. Under the optimum conditions, in t he concentration range of 0.08-8 mu g/ml of molybdenum, a quite linear curv e (r = 0.9991, n = 13) was obtained. The detection limit is 60 ng/ml. The r elative standard deviation of 10 replicate measurements is 1.6% for a 1-mu g/ml solution of Mo(VI). The proposed method was applied successfully to th e determination of Mo(VI) in plants. (C) 2000 Elsevier Science B.V. All rig hts reserved.