Hydrodynamic Sequential Injection with Stopped-flow Procedure for Consecutive Determination of Phosphate and Silicate in Wastewater

A hydrodynamic sequential injection system was proposed for the determination of phosphate and silicate in wastewater and fish pond water samples. It was based on the molybdenum blue method with spectrophotometric measurement at 710 nm. Stopped-flow procedure was applied in order to increase the reaction time. Two calibration graphs, one for the determination of phosphate concentration and another for phosphate plus silicate concentration were established in the range of 0.1 - 4.0 mg L-1 and 1.1 - 12.0 mg L-1, respectively, with a detection limit (3 sigma) of 80 mu g P L-1 and 90 mu g Si L-1. Sample throughput was 20 h(-1) for consecutive determination of both analytes. Contents of phosphate and silicate found in wastewater samples by the developed method were in good agreement with those obtained by a batch spectrophotometric method.