AMPEROMETRIC PH REGULATION - A FLEXIBLE TOOL FOR RAPID AND PRECISE TEMPORAL CONTROL OVER THE PH OF AN ELECTROLYTE SOLUTION

Temporal control over both pH and ionic strength of an electrolyte sol ution with high accuracy was achieved with a dynamic, computer feedbac k-centrolled amperometric pH-stat device consisting of four pH-regulat ing electrodes placed in electrolyte reservoirs that are separated by dialysis membranes from a central compartment. Theoretical predictions of the behavior of this arrangement, obtained by computer simulation, were validated by running temporal pH programs such as step functions , oscillations, and linear pH gradients. Deviations from nominal value s given by the computer program are within the limits of accuracy of t he pH-measuring electrodes. No volume changes accompany a change of pH or conductivity since ions are forced to leave or enter the central c ompartment through the membranes by the electrical force applied betwe en the pH-regulating electrodes. The device is flexible, easy to use a nd easily miniaturized. We discuss a wide range of possible applicatio ns in biochemistry and cell science. These include automated pH adjust ment, isoelectric protein separation, amperometric measurement of enzy me kinetics and the response of cell cultures to well-defined pH chang es.