Spectrophotometric Determination of Trace Amounts of Molybdenum in Aqueous Solution with Thiocyanate-Acridine Red-Polyvinyl Alcohol

A highly sensitive spectrophotometric method for determination of Mo(Ⅵ) has been developed, based on Mo(Ⅵ) reduced by thiocarbamide-ascorbic acid and Fe(Ⅲ) as catalyst in sulphuric acid solution to form Mo(Ⅴ), then to form [MoO(SCN) 5] 2- in an excess of thiocyanate, the formation of the 1:2 ion-association complex of [MoO(SCN) 5] 2 with acridine red in the presence of polyvinyl alcohol. The molar absorptivity is 1.68×10 5 L·mol -1 ·cm -1 . The maximum absorbance of ion-association against reagent blank is at 585nm. Beer's law is obeyed the range of 0～9mgMo(Ⅵ)/25mL. The procedure is relatively simple, and eliminated interference achieved by added the mixed masking agent of 20% sodium potassium tartrate-10% oxalic acid into sample solution, so the determination has very good selectivity. Trace Mo(Ⅵ) in water and biomaterial can be satisfactorily determined directly in aqueous solution by the method.