Simultaneous determination of silicate and phosphate in boiler water at power plants based on series flow cells by using flow injection spectrophotometry Original Research Article

A new flow injection spectrophotometric method is described for the simultaneous determination of silicate and phosphate. Effects on the sensitivity of the method of the wavelength, temperature, length of reaction coils, pump rates, acidity, sampling volume, concentration of the chromogenic reagent, etc. were also investigated. The optimum conditions were ascertained. The principle of the method is that total concentration of silicate plus phosphate is determined when a injected sample plug is passing through the first flow cell and then the concentration of silicate is serially) determined at a second flow cell of the same detector after continuously masking the yellow molybdophosphate in the sample zone. Finally, the concentration of phosphate is obtained by difference. Silicate and phosphate are determined in boiler water at power plants; 60–120 samples h−1 be analyzed. Determination ranges are 0.05–22 mg l−1 for silicate and 0.1–24 mg l−1 for phosphate. Relative standard deviations for metasilicate and orthophosphate were ≤1.2 and 1.3%, respectively. Recovery ranges of silicate and phosphate in the samples are 98–103%.