Simultaneous determination of phosphate and silicate ions based on the formation of molybdenum blue by FIA

Abstract

A flow injection system for simultaneous determination of phosphate and silicate ions based on the formation of molybdenum blue is developed. This system is based on the difference of sulfuric acid concentration between phosphate and silicate on the formation of molybdenum blue. In this system, a part of sample zone in carrier is mixed with sulfuric acid solution and then, high and low concentrations of sulfuric acid zones are formed in the sample zone. In the low concentration zone, phosphomolybdenum, silicomolybdenum and isopolymolybdenum blues are formed. In the high concentration zone, only phosphomolybdenum blue is formed. Phosphate and silicate ions are determined by the difference of absorbance (830 nm) between high and low concentration zones. The determination limit of phosphate ion estimated was 0.003 mg L-1 as P and that of silicate ion was 0.04 mg L-1 as Si. The analysis rate was 6 samples h-1. This system was available for phosphate and silicate ions in the sea water. © 2010 The Japan Society for Analytical Chemistry.