A frequency-response equalization technique for improved measurement of rapid ional and electrical signals with pH-microelectrodes

Electrical and ional activity changes in small cells, e.g. in neurons, are usually measured with fine tip-sized double barreled microelectrodes with one channel filled with a liquid ion-exchanger. These signals are distorted by the limited bandwidth of this sensor; furthermore, the transfer function of the electrode is different for each signal. We describe two techniques developed to equalize both transfer functions by adjusting the output signal of the electrode to a defined electrical and ional input function. A test-system allows the pH to be switched within a few msec. Using this equalization technique results in an improved performance of the pH-electrode with a 90% response time of 60 ms after a pH step.