DETERMINATION OF DISSOLVED REACTIVE PHOSPHORUS IN ESTUARINE WATERS USING A REVERSED FLOW-INJECTION MANIFOLD

The Schlieren or refractive index (RI) effect is a major problem in th e determination of dissolved reactive phosphorus in estuarine waters u sing conventional flow injection (FI) manifolds with sample injection, This is because differences in RI between the injected sample zone an d the carrier stream give rise to a lensing effect which is superimpos ed on the blank response and causes significant error in quantitation, A simple reversed flow injection (rFI) manifold using spectrophotomet ric detection which removes these quantitation errors is reported, Aci dic molybdate is injected into a sulfuric acid carrier stream of the s ame refractive index and sequentially merged with sample and reductant (ascorbic acid), Reduction of phosphomolybdate to phosphomolybdenum b lue is carried out in a coil thermostated at 60 degrees C. Dissolved r eactive phosphorus has been successfully determined in estuarine water s with salinities ranging from 0 to 30 parts per thousand using calibr ation standards prepared in deionized water, with a detection limit of 2 mu g l(-1) PO4-P and a linear range of 2-100 mu g l(-1) PO4-P (r(2) = 0.9998).