Determination of trace amounts of phosphate in water samples by ion-exchange resin thin-layer spectrophotometry

A simple but highly sensitive method for determining trace amounts of phosphate in water has been developed. The method involves concentrating molybdenum blue in a thin layer prepared from a finely divided anion-exchange resin and measurement of the absorbance of the coloured layer. The dependence of the absorbance on the concentration of sulphuric acid and ammonium molybdate resulting from the procedure for producing molybdenum blue was reduced by adding gelatin to the sample solution. The calibration graph deviated slightly from linearity and the relative standard deviation was 1.95%(n= 4) for 0.5 µg of phosphate. This method was applied to the determination of trace amounts of phosphate in several water samples.