USE OF IMMOBILIZED 3-PHYTASE AND FLOW-INJECTION FOR THE DETERMINATIONOF PHOSPHORUS SPECIES IN NATURAL-WATERS

A proportion of dissolved organic phosphorus (DOP) compounds found in natural waters may be utilized by algae and bacteria through hydrolysi s by extracellular phosphomonoesterases such as alkaline phosphatase. The fraction of DOP remaining unhydrolysed may consist of organic phos phorus species such as myo-inositol hexakisphosphate (phytic acid), an d comprise part of the pool of biologically unavailable or even refrac tory DOP. Of this bio-unavailable DOP fraction, a major portion is ame nable to hydrolysis by 3-phytase, a phosphohydrolytic enzyme which is not found widely in aquatic systems. This paper describes the developm ent and application of a flow injection system which utilises immobili zed 3-phytase for the determination of phytase hydrolysable phosphorus (PHP) present in natural waters. The product of enzymatic hydrolysis is orthophosphate, and a conventional phosphomolybdenum blue detection method was used. The use of a suitable flow injection manifold and a multiple linear regression calibration procedure for quasi-simultaneou s determination of phytase-hydrolysable and dissolved reactive phospho rus (DRP) coexisting in natural waters is outlined. The proposed techn ique is rapid (ca. 40 injections h(-1)), sensitive and reproducible, a nd the immobilized phytase exhibited good operational and storage stab ility over a period of several months.