AUTOMATED, HIGH-PRECISION COULOMETRIC TITRIMETRY .1. ENGINEERING AND IMPLEMENTATION

Automated constant-current coulometry, based on Faraday's Laws, achiev es uncertainties (relative standard deviation) of less than 1 part in 20000 without chemical standardization. It is applicable to acid-base, redox, and precipitation titrations of high-purity compounds and solu tions. Automation of the technique permits unsupervised operation and reduces operator-dependent errors. Initial setup and sample introducti on are the sole manual steps. Each assay consists of a main titration at high, constant current, bracketed by the initial and final endpoint routines, each at a lower current. The coulometric assay is analogous to a conventional titration in which two different concentrations of the titrant are used to attain optimum accuracy. The initial endpoint determination corresponds to the blank determination in a classical ti tration. Each titration includes a statistical analysis of the random and systematic uncertainties associated with the analysis. Individual steps in the procedure are performed by a hierarchical series of subro utines to reduce program complexity. Results are presented for K2Cr2O7 , benzoic acid, and solutions of strong acids.