Spectrophotometric determination of phosphorus in steel by rhodamine B-molybdovanadophosphoric heteropoly acid system

A spectrophotometry for the determination of phosphorus in steel samples by colour reaction of rhodamine B with phosphorus-vanadium-molybdenum heteropoly acid in O/W nonionic microemulsion( OP/n-C5H11OH/n-C7H16/H2O) medium was established. The dosage of reagents was optimized. The maximum absorption wavelength of the association complex of rhodamine B with phosphorus-vanadium-molybdenum heteropoly acid was at 585nm. Beer′s law was obeyed in the concentration range of 0.015-0.10μg/mL for P . The linear regression equation was A=0.095 6ρ-0.038 2. The apparent molar absorptivity was 1.48×105 L·mol-1·cm-1. Most common ions did not interfere with the determination . The interference from Cu2+ was removed by adding EDTA. The method was applied to the determination of phosphorus in standard steel samples and the results were consistent with certified values with RSD of 1.2%-3.5%