Determination of phosphate in surface water of lopburi province using a simple flow injection analytical system

Abstract

A simple flow injection analytical system for an automatic determination of phosphate in water samples using the molybdenum blue method was developed. Samples were injected and mixed with ascorbic acid used as a reducing agent. The absorbance of the resulting molybdenum blue complex was measured at 880 nm by a spectrophotometer. The optimal conditions of this system were 2 mL/min of carrier flow rate, 1,000 μL of sample volume, 60 centimeters of mixing tube length, and 0.020 mol/L of ascorbic acid. The proposed method showed reliability, high sensitivity, spend small amount of reagents and samples, and fast sample throughput (52 samples/hour). The limit of detection (LOD) was 0.015 mg P/L of phosphate. Precision obtained injecting a phosphate standard solution of 0.50 mg P/L (n=10) was 1.81%. This system can be applied to determination of phosphate content in surface water samples in Lopburi province by comparing with a standard method. It was found that obtained from the developed system agreed well with the standard method using the pair t-test (tstat 0.04 < tcrit 2.36). This flow injection analysis system has no effect from arsenate and silicate interference for the analysis of natural water samples.