Amperometric sensing system for the detection of urea by a combination of the pH-stat method and flow injection analysis

A new type of amperometric sensing system for urea was constructed based on combining the pH-stat method and the flow injection analysis (FIA) to solve the problem of potentiometry of dependency on the buffer concentration to the response of urea and moreover to eliminate the response to interfering substances. In the new system, the response to urea was independent of the buffer concentration and the relation between current response and urea concentration became linear. The possibility of automatic operation of this system with a potentiostatic feed back circuit was also confirmed. In this system, the relationship between urea concentration and current response was found to be linear up to 600 μM (=6.0×10−4 mol dm−3). Since the sample path was separated from the electrolysis path, no current response of interfering substances such as ascorbic acid and uric acid occurred at the physiological level. Thus, the possibility of amperometric sensing of urea which has a merit of no dependency on the buffer concentration and moreover no influence of interfering substances was demonstrated.