The mechanism of formation and reduction of 12 molybdi-phosphoric acid

Abstract

Investigation of the chemical reactions involved in phosphate analyses which are based on the method of Fiske and Subbarow revealed the existence of two distinct species of 12 molybdi-phosphoric acid (12 MPA). One of these species (designated β) was characterized by a distinct absorption maximum at 310 nm whereas the other form (designated α) exhibited absorption bands only in the far ultra-violet. α-12 MPA was reduced only by an acid solution of stannous chloride whereas β-12 MPA was reduced even by mild reductive conditions. Reduction of β-12 MPA by high concentrations of reductors, such as metol and ascorbate, led to the detection of a previously undescribed reduction product. This product has a higher molar absorption coefficient than the ‘molybdenum blue’ complexes reported so far. The application of these findings to the development of a simple and fast method for the quantitation of phosphate is discussed.