Automatic coulometric titration with photometric end-point detection : Part I. A coulometric titrator based on differential photometric detection

Abstract

A system for automatic coulometric titrations with photometric end-point detection is described. To compensate for errors caused by gas bubbles and turbidity, the beam is split after passing the titration cell. The intensities of the respective light beams are registered by means of two photodiodes operating in the current mode. The currents are converted to voltages and the logarithm of the quotient is taken. The measured absorbance is only slightly dependent on the variation in the intensity of the incident light. A diminution of one absorbance unit causes a relative error of less than 5%. The deviations due to carbon particles (37–75 μm) were less than 0.002 absorbance units per mg of carbon present in 10 ml of solution. The improvement with respect to errors caused by gas bubbles is illustrated. The fundamental advantage of a one-lamp system over a twolamp system is shown.