Lester P. Rigdon

Automated potentiometric analysis with selective electrodes

Abstract An automated potentiometric analyzer based on a residual-chlorine electrode has been developed that can determine chlorine concentrations of a 4–75 ppb (±2 ppb, standard deviation 0.6–1.9 ppb). A microcomputer-controlled digital buret delivers a predetermined number of aliquots of standard, and the electrode measures the potential of the test solution after each addition. An arithmetic processing unit transforms the acquired potentiometric data to the Gran (antilog) domain; the microcomputer then calculates a set of equivalence-point estimates and, using an error function criterion, selects the best estimate. The instrument includes a digital buret, 8080 microcomputer, arithmetic processing unit, real-time clock, video display, and 16-character key pad; it uses a modified version of the computer language BASIC compiled and programmed into Programmable Read-Only Memory (PROM). Although this system was designed to assay residual chlorine in water, the analyzer can also function as a digital pH (or millivolt) meter or, with minor software modifications, serve as a general-purpose instrument using any appropriate electrode system.