Simultaneous Spectrophotometric Determination of Silicate and Phosphate by Flow Injection Analysis

Abstract A method is reported for the simultaneous determination of phosphate and silicate by flow injection analysis based on the different rate of formation of the heteromolybdic acids of the two anions. Measurements are based on the colour of the ion-pairs formed between the said molybdic acids and Rhodamine B. The method allows the determination of the two anions at a rate of 20 samples/h over the ranges 0.05–2.5 ppm (phosphate) and 0.8–15 ppm (silicate), which allows application to a variety of waters.