AMMONIUM DETECTION USING AN ION-SELECTIVE ELECTRODE ARRAY IN FLOW-INJECTION ANALYSIS

An ammonium detection system using ion-selective electrodes (ISEs) in flow-injection analysis (FIA) is described. Because of the low selectivity of the nonactin ammonium selective electrode toward some common ions, notably potassium, different selectivity enhancement techniques have been examined. An array of ISEs selective for ammonium, sodium, potassium, and calcium was used as the FIA detector, and the array response was modeled via the Nikolskii-Eisenmann equation and the Projection Pursuit regression model. The interfacing of the system to a PC-386SX computer using an Analog Devices RTI-815 I/O card is also described. The results show that the use of an array of ISEs under FIA regimes for the detection of ammonium in the activity range 10 to 0.01 mM,gives much improved results for the determination of ammonium in aqueous samples than the use of a single ammonium electrode. The 'performance of the array under steady-state and FIA conditions is compared.