Determination of trace phosphorus in organic materials by a combined low temperature ashing-spectrophotometry

Abstract

Less than 10 μg or 10 ppm phosphorus in organic materials was determined by a low-temperature ashing-molybdenum blue spectrophotometry. After a sample had been treated by low-temperature asher, the residue was taken up and fumed with 15 cm3 of 30 (w/w)% perchloric acid. After cooling the perchlonic acid solution was transferred to a 300 cm3 separatory funnel, to which 10 cm3 of 5 (w/v)% ammonium molybdate was added and the mixture was diluted to 100 cm3 with water. Phosphorus was extracted into 10 cm3 of butyl acetate by shaking the mixture for 1 min. The organic phase was transferred to a 25 cm3 volumetric flask and was diluted with ethanol to the mark. After the addition of 0.2 cm3 of 5 (w/v)% tin(II) chloride, the absorbance was measured at a wavelength of 725 nm against water. Results on the determination of phosphorus in rice and filter papers were quoted and compared with those by other ashing methods. Recoveries were checked with tetraphenylphosphonium chloride, yielding 95.4% as an average. © 1979, The Japan Society for Analytical Chemistry. All rights reserved.