Light scattering method for the determination of trace amounts of phosphate using a cationic water-soluble porphyrin

Abstract

A sensitive and simple method is described for the determination of phosphate at the ppb level based on light scattering of the ion pair formed by the reaction of molybdophosphate with tetrakis(1-methyl-pyridinium-4-yl)porphyrin (H₂tmpyp⁴⁺). The light scattering intensity was measured in the range 300–800 nm under irradiation by a spectrofluorimeter and the maximum intensity was observed at 475 nm. The molar ratio of H₂tmpyp⁴⁺ to molybdophosphate was 1:1 in sulfuric acid. Cations and anions usually encountered in natural water, including silicate and chloride (0.5 mol dm^–3), did not interfere with the determination of phosphate. The proposed method was applied to the determination of phosphate in river, sea- and tap water samples.