Ultra-Trace Determination of Phosphate Ion Based on Filtration-Dissolution and Flow-through Spectrophotometric Measurement

A sensitive spectrophotometric method for the determination of ultra-trace amounts of phosphate ion is proposed. The colored ion associate formed between molybdophosphate and Malachite Green (MG) was filtered through a tiny membrane filter (cellulose nitrate; poresize, 1.0μm; 9mm diameter), dissolved together with the membrane filter in 1cm(3) or less of Methyl Cellosolve; the absorbance of the solution was then measured at 627nm with a flow-through system equipped with an autosampler. The absorbance, the standard deviation and the relative standard deviation of the reagent blank were 0.0270, 0.0005 and 1.8%, respectively. A calibration graph was linear over the range from 0.018 to 1.0ng cm(-3) (1ppb) of phosphorus using 40cm(3) of sample solutions; the detection limit corresponding to two-times the standard deviation of the reagent blank was 3ppt of phosphorus. By using the proposed method, phosphate ion in pure water samples were determined.