Fluorimetric differential-kinetic determination of silicate and phosphate in waters by flow-injection analysis

A flow-injection analysis (FIA) method for simultaneous determination of silicate and phosphate, based on the different rates of formation of their molybdate heteropoly acids is suggested. The fluorimetrically monitored product is thiochrome, formed by oxidation of thiamine by the heteropoly acid. The FIA configurations designed allow performance of two measurements at different times on each sample injected. The method permits the determination of these anions in the range 30-600 ng ml in ratios from 1:10 to 10:1 and can be applied to samples of running and bottled water with good results. The sampling frequency achievable is 60 hr .