Simple kinetic method for assay of menadione in pharmaceuticals

A new simple and sensitive kinetic method for determining menadione in pure form and injection form is described, based on the reaction between menadione and sodium hydroxide to form a colored complex with a strong absorbance at 450 nm. The method is valid for determining menadione at concentrations ranging from 5.807 x 10(-1) to 7.549 x 10(-3) M. The complex forms at a 2:3 concentration ratio of menadione with respect to sodium hydroxide. The formation constant is 8.37 x 10(15), and the molar absorptivity is 6.55 x 10(2) L/mol.cm. The precision and accuracy of the method and the effect of interfering substances were studied. Results were compared with those obtained with an official method.