DESIGN AND PROPERTIES OF A FLOW-INJECTION ANALYSIS CELL USING POTASSIUM-SELECTIVE ION-SENSITIVE FIELD-EFFECT TRANSISTORS AS DETECTION ELEMENTS

The combination of flow-injection analysis (FIA) and chemically modified ion-sensitive field-effect transistors (CHEMFETs) is described. In a wall-jet cell, two identical potassium-selective CHEMFETs were used for a differential measurement using a platinum (pseudo-)reference electrode. Silicone-rubber membrane materials, chemically bound to the SiO2 gate oxide, were used with valinomycin as the ionophore. The optimized FIA system showed a linear response of 56 mV per decade for potassium concentrations above 5 x 10(-5) M. Preliminary results of potassium determinations in human serum and urine samples are presented.