Instrument for Coulometric Titrimetry with Feedback-Controlled Electrolysis Current

SUMMARY A novel coulometric titrator is described that provides continuously variable, feedback-controlled electrolysis current. The feedback signal is proportional to the first time derivative of the indicator electrode potential. The result of this type of control is a titration in which the electrolysis rate is minimal in end point regions and maximal between end points; this keeps the chemical system in quasiequilibrium throughout the titration, yields excellent titration curves, and facilitates measurement of integrator potentials at the end points. The performance of this instrument is illustrated by the coulometric titration of iron in the presence of a cerous sulfate-sulfuric acid intermediate.