Optimisation of the micro-scale determination of phosphates by direct potentiometric titration with silver ions and its application to the determination of phosphorus in organic compounds

The micro-scale determination of orthophosphate ions by argentimetric titration with potentiometric detection of the end-point using a combined massive silver electrode was investigated. The best results were obtained when this titration was carried out in water-isopropanol (50%V/V) buffered at pH 8.80. Under such conditions the titration error arising from the partial coprecipitation of silver oxide near the equivalence point is minimised and the results obtained have a satisfactory accuracy (errors within ±0.30%) and good reproducibility. The concentration range in which reasonable accuracy and precision are attained and the most suitable titration rate to be adopted when an automatic titrimetric device is used were also considered. This optimised titration method was successfully applied to the determination of phosphorus in organophosphorus compounds after mineralisation in a suitably modified Schöniger flask.