Flotation-spectrofluorimetric determination of phosphate in natural water using Rhodamine B as an ion-pair reagent

Abstract

A sensitive and accurate spectrofluorimetric method is described for the determination of phosphate in natural water using Rhodamine B as an ion-pair reagent. A Rhodamine B-molybdophosphate ion pair was floated as a membrane-like substance at the phase boundary between the aqueous phase and a diethyl ether phase. After the aqueous phase had been discarded, the excess of Rhodamine B extracted into the diethyl ether was removed by shaking with 25 ml of 1.0 M hydrochloric acid. The floated ion pair was dissolved by the addition of methanol to the diethyl ether phase. The determination of phosphate was performed by measuring the fluorescence intensity of the organic phase at 573 nm with excitation at 554 nm. The calibration graph was linear up to 0.25 µg of phosphorus with a correlation coefficient of 0.999. Although arsenic(V) caused a positive error, no ions commonly existing in natural water, including silicate, interfere with the determination of phosphate. The proposed method was applied to the determination of phosphate phosphorus in some natural water samples.