Application of gallein in the presence of benzyldimethyldodecylammonium bromide for spectrophotometric determination of molybdenum in steel

A simple and direct method for spectrophotometric determination of molybdenum(VI) in steel, based on the formation of a coloured complex of Mo(VI) with gallein (Gal) in the presence of benzyldimethyldodecylammonium bromide (BDDA), has been developed. Optimum pH and the concentrations of Gal and BDDA ensuring maximum absorbance have been determined. The Mo-Gal-BDDA complex showed a maximum absorbance at 617 nm with molar absorptivity epsilon = 4.69 x 10(4) L mol(-1) cm(-1). Beer's law was obeyed within molybdenum concentration range 0.08 divided by 0.80 mu g mL(-1). The influence of several interfering ions has been discussed. The stoichiometry of the complex under optimum conditions was established as Mo:Gal = 2:3 by applying Job's method. The proposed method has been applied to the determination of molybdenum in steel and Armco iron. To evaluate the accuracy of the elaborated method, the determined content of Mo was compared to the declared value as well as to the result obtained by the reference ICP-OES method.