Amplification method for the spectrophotometric determination of phosphorus

An amplification method with ion-exchange pre-separation for the spectrophotometric phosphorus determination in various alloys is described. Phosphorus is converted into molybdophosphoric acid, separated by selective extraction and back-extracted into the aqueous phase. The molybdenum is liberated by alkaline decomposition of the heteropoly acid. The spectrophotometric measurement is based on the reaction of molybdenum(VI) with 2,2-biquinoxalyl. High molar absorptivity of 1,1-dihydro-2,2-biquinoxalylene (=3.3 · 10⁴ L mol^–1 cm^–1) and the twelve-fold amplification guarantee high precision and makes the determination of phosphorus in the 1–6 g level possible.