POTENTIOMETRIC FIA SYSTEM WITH REACTOR BASED ON NATURAL UREASE SOURCEAND TUBULAR DETECTOR OF AMMONIUM-IONS - DETERMINATION OF UREA IN FERTILIZERS

An FIA system was developed to analyze urea by monitoring ammonium ion s generated by enzymatic degradation with a tubular ion-selective elec trode containing nonactin on polyvinyl chloride (PVC) membrane. As an urease source, 120 mg of the leguminous canavalia brasiliensis were im mobilized in an enzymatic reactor with glutaraldehyde. Ammonium ions a re converted to ammonia by an alkaline solution, 1 mol l(-1) NaOH, and permeates through a polytetrafluoroethylene membrane until the detect or. The method can be used in an urea concentration range of 2.5X10(-4 ) to 2.5X10(-3) mol l(-1) (25.0 degrees C). Analysis of 25 mu l commer cial samples of fertilizers, showed a relative error of 0.2% with a hi gh selectivity to the species present.