Spectrophotometric Determination of Trace Phosphate with Preconcentration of Molybdophosphate-Malachite Green Aggregate by Filtration through Membrane Filter

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Abstract
A simple and rapid method for the determination of trace amounts of phosphate in water was proposed. The addition of phosphate to a mixture solution of ammonium molybdate and malachite green resulted in a blue green coloration due to the formation of molybdophosphate aggregate with malachite green in 0.45 M H2SO4. The aggregate was collected on a nitrocellulose-acetylcellulose membrane filter (0.45 .mu.m pore size), and dissolved in a small volume of methylcellosolve together with membrane filter. The absorbance at 627 nm was proportional to the concentration of phosphate with the molar absorptivity; 2.7 .times. 105 M-1 cm-1. The present method made it possible to determine phosphate in amount ranging from 0.3 to 30 ppb phosphorus. The coefficient of variation was 3.66% in the determination of 18 ppb phosphorus. The analytical recoveries of phosphate in tap water and river water were 100.2% and 104.7%, respectively.

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