A sensitive and selective spectrophotometric procedure for the determination of phosphorus

Abstract

Phosphorus as phosphate is determined by an amplification procedure in which the heteropoly acid H₃PO₄(MoO₃)₁₂ is formed and extracted away from excess of molybdate reagent. The 12 molybdate ions associated with the phosphate are then determined spectrophotometrically at 710 mµ as the green molybdenum(VI) complex with 2-amino-4-chlorobenzenethiol in chloroform. Depending on the procedure used, the effective molar absorptivity for phosphorus is 96,900 or 359,000. The proposed procedure is therefore much more sensitive than previously described methods for phosphorus. Amounts of phosphorus down to 0·2 µg (0·008 p.p.m.) may be determined. Large excesses of silicon, germanium, arsenic or antimony do not interfere. A simple masking procedure obviates any interference from up to a 30-fold excess of tungsten(VI).