Direct Spectrophotometric Determination of Phosphonate and Diphosphate Ions Based on the Formation of Heteropoly Blue Complexes

A simple spectrophotometric method is proposed for the direct determination of PHO 3 2- and P 2 O 7 4- ions. In acidic solutions containing 50%(v/v) CH 3 COCH 3 , the Mo(VI)-Mo(V) reagent reacts directly with PHO 3 2- and P 2 O 7 4- ions to form the respective heteropoly blues. The amounts of mixed-valence blue species thus formed depended linearly on the PHO 3 2- and P 2 O 7 4- concentrations in the ranges 1X10 -5 - 1X10 -3 M and 2X10 -5 - 2X10 -4 M, respectively. Interferences from foreign ions are also discussed.