Determination of phosphorus in steel by precipitation as silverphosphate and subsequent determination by spectrophotometric method

Presence of phosphorus in steel is due to impurities coming from iron making process. Phosphorous in steel has been determined by dissolution in 1:1 (v/v) HNO3 followed by complexation of iron matrix by EDTA at pH 4. Phosphorus is precipitated with silver nitrate solution producing a yellow colored silver orthophosphate (Ag3PO4). The precipitate is redissolved in dilute nitric acid (1:10 v/v). A complex of phospho-vanado-molybdic acid is formed which is measured (440 nm) colorimetrically. Interference from Cr(VI) is eliminated by reducing it to Cr(III). Tungsten interferes in the estimation, whereas, vanadium (5 wt. %) and molybdenum (1.5 wt. %) containing steel can be estimated. Several BCS steel samples have been estimated with RSD value of 4.0%. This method has been applied in the chemical analysis of several steel samples submitted to the laboratory. The results were compared with IS and ASTM method of analysis and the RSD value of analysis is between ±4.0 %.