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Clinical Chemistry 17: 214-221, 1971;
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Clinical Chemistry, Vol 17, 214-221, Copyright © 1971 by the American Association for Clinical Chemistry

A Digital pH Stat for Automated Kinetic Analysis

Raymond E. Karcher 1 and Harry L. Pardue 1

1 Department of Chemistry, Purdue University, Lafayette, Ind. 47907.

A "pH stat" that spectrophotometrically monitors pH and electrolytically generates either acid or base has been developed to follow the rates of certain enzyme-catalyzed reactions. The pH is monitored by coupling a pH indicator to the main reaction. As reaction proceeds, the instrument coulometrically pulses titrant into the photometer cell as required to maintain a constant pH. Generation is accomplished with Pt and Ag-AgCl electrodes. Constant-current conditions are used so that a given number of pulses corresponds to a constant reaction interval. A series of flip-flops counts the pulses as they occur; a timing circuit records the time required to generate a set number of pulses. A reciprocal time computer provides automated readout in units of absolute enzyme activity. Initial experiments on the acetylcholinesterase system (pH 7.60) show linear enzyme dependence curves with scatter of 2% or less. The change in pH during a single cycle is less than 0.05 units and the precision for replicate samples is about 2%.


Key Words: acetylcholinesterase system • total serum cholinesterase • potentiometric-photometric pH change measurements, sensitivity compared • automated enzyme reaction-rate or activity determination

Submitted on October 23, 1970
Accepted on January 7, 1971






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Copyright © 1971 by the American Association for Clinical Chemistry.