Masahiko Kan

Determination of phosphate, arsenate and arsenite in natural water by flotation-spectrophotometry and extraction-indirect atomic absorption spectrometry using Malachite Green as an ion-pair reagent

Sensitive and accurate methods are described for the determination of phosphate, arsenate and arsenite in natural water using Malachite Green as an ion-pair reagent. The ion pair of Malachite Green with molybdophosphate is floated as a membrane-like substance at the phase boundary between the aqueous phase and a diethyl ether phase. After discarding the aqueous phase, methanol is added to dissolve the floated ion pair. The determination of phosphate is performed by measuring the absorbance of the organic phase. The apparent molar absorptivity of phosphate is 3.3 × 105 l mol–1 cm–1 at 620 nm. Arsenate is also determined using the same procedure. An oxidative or a reductive reaction of arsenic with potassium dichromate or sodium thiosulphate is utilised for the determination of phosphate, arsenate and arsenite. An extraction-indirect atomic absorption spectrometric determination method was also developed in which the atomic absorption of molybdenum in the ion pair of Malachite Green with molybdophosphate is measured. The proposed methods were applied to the determination of phosphate, arsenate and arsenite in some natural water samples.

Indirect atomic-absorption spectrophotometric determination of phosphorus after flotation as the ion-pair of molybdophosphate with bis[2-(5-chloro-2-pyridylazo)-5-diethylaminophenolato]cobalt(III).

An atomic-absorption spectrophotometric method has been developed for the indirect determination of phosphorus. The calibration graph is linear over the range 0.025-0.2 mug of phosphorus. The relative standard deviation is 1.3% for 0.2 mug of phosphorus (6 replicates). The method has been applied to the determination of phosphate in natural water samples. The enhancement effect of acetone on the determination is discussed.

Determination of phosphate by flotation-fluorophotometry using ion-pair of molybdophosphate with Rhodamine 6G

SummaryA highly sensitive and accurate fluorophotometric method is described for the determination of phosphate using the ion pair formation of molybdophosphate with Rhodamine 6G. This ion pair is floated at the phase boundary between ethyl ether phase and aqueous phase when the aqueous phase is adjusted to 0.38 mol/l sulphuric acid, 1.9 mmol/l ammonium molybdate and 3.8 Μmol/l Rhodamine 6G. After the phase separation, the floated ion pair is dissolved into the ethyl ether phase by the addition of methanol. The fluorescence intensity of the ion pair is measured at 548 nm with excitation at 530 nm. The calibration curve for phosphate is linear up to 100 ng of phosphorus with a correlation coefficient of 0.999. The relative standard deviation is 2.3% for 100 ng of phosphorus (n=11). Although arsenic(V) causes 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 waters and satisfactory results were obtained.