Determination of phosphate in water samples

Abstract

Orthophosphate and molybdate ions condense in sulphuric acid solution to give molybdophosphoric acid, which upon selective reduction with hydrazinium sulphate produces a blue color due to molybdenum blue. This was readily conjugated with the cation dye Brilliant Blue, which exhibits maximum absorption after its extraction in chloroform at 840 nm. Beer's law is obeyed in the concentration range of 2.8 to 28.1 μg phosphate per 25 ml, with molar absorptivity 883700 L mol-1 cm-1. This procedure was compared with the results obtained from titrimetric techniques. A potentiometric method was used in the presence of a cupric ion selective electrode to determine the excess copper ions with EDTA after phosphate precipitation. The excess in copper ions was determined amperometrically using thiomalic acid in acetic acid as a titrant at an applied voltage of +0.8V versus a standard calomel electrode, with a rotating micro platinum electrode.