Spectrophotometric determination of molybdenum in steels with o-nitrophenylfluorone and cetyltrimethylammonium bromide.

A method has been developed for determining microamounts of molybdenum(VI) in aqueous solution by means of the Mo-o-nitrophenylfluorone-cetyltrimethylammonium bromide system, in which micellar solubilization is applied. A red complex is formed in 0.2-0.6M hydrochloric acid medium. The sensitivity of the method is high, and the apparent molar absorptivity is 1.55 x 10(5) l.mole(-1). cm(-1). The absorption peak of the complex appears at 530 nm. The colour of the complex develops quickly and is stable for more than 24 hr. The composition of the complex is Mo: o-NPF = 1:1, and the system obeys Beer's law in the range 0-10 mug of Mo per 25 ml. The method has been used for the rapid determination of molybdenum in alloy steels with satisfactory results.