ELIMINATION OF THE SCHLIEREN EFFECT IN THE DETERMINATION OF REACTIVE PHOSPHORUS IN ESTUARINE WATERS BY FLOW-INJECTION ANALYSIS

Conventional flow-injection manifolds with sample injection for the de termination of reactive phosphorus in estuarine waters are limited by the Schlieren or refractive index (RI) effect which can cause major er rors in quantification. A simple flow-injection (FI) manifold which ob viates this RI error in reactive phosphorus measurement is reported. I t involves the injection of acidic molybdophosphate reagent into a car rier stream of sodium chloride solution of similar refractive index, w hich is then sequentially merged with a sample (the salinity of which may vary widely from sample to sample) and a reductant. Despite the oc currence of sizeable blank signals, reactive phosphorus has been succe ssfully measured in samples with salinities ranging from 0 to 34 parts per thousand using calibration standards prepared in deionised water, with a detection limit of 6 mu g l(-1) P. (C) 1997 Elsevier Science B .V.