Spectrophotometric determination of phosphorus as orthophosphate based on solvent extraction of the ion associate of molybdophosphate with malachite green using flow injection

Abstract

Phosphorus as orthophosphate in water was determined by a spectrophotometric method involving flow injection coupled with solvent extraction. The ion associate formed between molybdophosphate and Malachite Green was extracted into benzene-4-methylpentan-2-one (1 + 2 V/V) and the absorbance was measured at 630 nm. The carrier stream was 0.005 M sulphuric acid and the reagent stream contained ammonium molybdate, Malachite Green and sulphuric acid. A newly designed phase separator was used to separate the organic phase. The sampling rate was 40 samples per hour. Calibration graphs were linear below 30 ng ml–1 and below 1 µg ml–1 of phosphorus on injecting samples of 300 and 10 µl, respectively. The detection limit was 0.1 ng ml–1 of phosphorus. Phosphorus in river water was determined satisfactorily by the proposed method.