DETERMINATION OF PHOSPHATE AS AGGREGATES OF ION ASSOCIATES BY LIGHT-SCATTERING DETECTION AND APPLICATION TO FLOW-INJECTION

Trace amounts of phosphate were determined by detecting the light-scat tering intensity with a spectrofluorimeter. The ion associate of molyb dophosphate with a chloro derivative of Malachite Green (CI-MG) or Rho damine B (RB) formed aggregates in an acidic solution before precipita ting. The formation rates of molybdophosphate and its ion associate we re rapid, but that of the aggregate was relatively slow. To stabilize the aggregates and to prevent their precipitation in an aqueous medium , poly(vinyl alcohol) solution was added after the formation of the io n associate, The light-scattering intensity of the ion associate with CI-MG, which did not emit fluorescence, could be detected, The intensi ties were obtained at the same wavelength of emission as that of excit ation: 460 nm for CI-MG and 460 and 580 nm for RB. The diameter of the aggregate was determined to be mainly 650 nm by using a laser light-s cattering detector, The number of ion associates in the aggregate was roughly estimated to be 4.3 x 10(7), The calibration graph was rectili near up to 10(-6) mol dm(-3) phosphate in the batchwise method, The me thod was applied to flow injection, where the calibration graph was re ctilinear from 2 x 10(-7) to 1 x 10(-6) mol dm(-3) and the detection l imit was 6 x 10(-8) mol dm(-3), The average peak height for 8.0 x 10(- 7) mol dm(-3) phosphate was 9.6 cm and the RSD of five measurements wa s 1.1%, The sample throughput was 15 h(-1). Interferences from bulky a nd hydrophobic anions were slight.