High Performance Microcoulometry

Abstract

The purpose of this work is the development of microcoulometric cell for measurement of halogenide ions in the range of ng amounts. The main task in the innovation is to fulfil the need of sensitive halogene determination in the automated measurement of the so-called adsorbable organically bound halogens (AOX) in waters. The very low consumption of supporting electrolyte and the energy saving configuration is also important factors in designing of monitor operation. We developed a micro volume tube reactor, which can work continuously with peristaltic pumps feeding the supporting electrolyte and the sample. The tube cell allows the injection of liquid and gas samples without changing the cell construction. A three electrode type potentiostatic microcoulometer with a rotating Ag working electrode was built, which maintains a constant electrode potential of the working electrode to the reference electrode by the generation of silver ions through anodic dissolution. The halogenide ions in sample solution change the electrode potential of the working electrode. The potentiostatic controller circuit sets a current flowing between the Ag working (anode) and a counter electrode (cathode). This current generates silver ions from the working electrode, these ions precipitate the halogenide ions from the cell electrolyte and restore the potential of the working electrode. It was a further successful hydraulic development to achieve a microvolume cell, which accepts both gas and liquid samples in the same equipment. The developed microcoulometer system has high sensitivity and works reliable in a wide measuring range.