SIMULTANEOUS DETERMINATION OF PHOSPHATE AND SILICATE IN WASTE-WATER BY SEQUENTIAL INJECTION-ANALYSIS

A sequential injection analysis system for the simultaneous determinat ion of phosphate and silicate in waste water is proposed. The method i s based on the formation of yellow vanadomolybdophosphate and molybdos ilicate, respectively, in addition to the use of large sample volumes. The mutual interference between both analytes was eliminated by selec tion of the appropriate acidity and by sample segmentation with oxalic acid. The calibration graph for phosphate and silicate is linear up t o 12 mg l(-1) P and 30 mg l(-1) Si, respectively. The detection limits are 0.2 mg l(-1) P and 0.9 mg l(-1) Si. The method provides a through put of 23 samples h(-1) with a relative standard deviation < 1.4% for phosphate and < 4% for silicate. The method was found to be suitable f or the determination of these species in waste mater samples.