Low output impedance composite pH sensors were constructed by direct attachment of an impedance converter to laboratory purpose combined pH glass electrodes. The signal was transmitted in analog form by unshielded electric cable. The performance of new and aged composite pH sensors was determined by the multiple-point calibration method. In case of new electrodes, the slope and the response time, as well as the reproducibility, were insignificantly influenced by the converter attached (the mean slope values calculated for the six electrode group studied were 57.80 mV/pH for unmodified electrodes and 57.97 mV/pH for modified electrodes). The electrode response was not affected by the presence of various electromagnetic noise sources or by the input impedance value of the measuring instrument. The slope and the response time of aged sensors were considerably improved using the impedance converter. The response time decreased from about 150–180 sec to about 30 sec and the average slope value increased from 54.94 mV/pH, calculated for unmodified electrodes, to 56.96 mV/pH, for modified electrodes.
The miniaturization of glass electrodes