AN ISFET-BASED FLOW-INJECTION ANALYSIS SYSTEM FOR DETERMINATION OF UREA - EXPERIMENT AND THEORY

Preliminary work is presented on an ISFET-based flow injection analysis system for urea determination, which avoids the need for compromise between speed of response and sensitivity found in integrated EnFETs. The response is linear for 30 μl samples in the range 0-25 mM urea; the response time is around 30 s. Theory which calculates the distribution of protons between the various buffers present, assuming 100% conversion of urea, gives a good description of the response and allows optimisation of the system to reduce interference by sample buffer and pH variations. © 1990.