Complex-forming equilibria in ion chromatography

Determination of equilibrium constants from chromatographic and electrophoretic measurements

Chemical interactions, such as acid-base, complex-forming, ion association and other equilibria, are widely exploited to improve the separation efficiency in liquid chromatography as well as in electrophoresis. On the other hand, these techniques can be advantageously used to study the chemical equilibria affecting the separations. If the equilibium is sufficiently fast in comparison with the separation process, then the retention characteristics in chromatography (retention factors) or the migration characteristics in electrophoresis (effective mobilities) may be expressed as functions of the composition of mobile phase or background electrolyte (BGE), respectively. Using a proper experimental arrangement, the dependencies of retention (migration) characteristics on the mobile phase (background electrolyte) composition can be measured and utilized to calculate the equilibrium constants for equlibria taking place in the mobile phase (background electrolyte). Although principles of these measurements have been known for a long time, only more recent studies utilizing HPLC and capillary electrophoretic techniques are reviewed in this paper.

Determination of some pesticides and intermediates by ion chromatography

We explored the possibility of determining some pesticides and process intermediates by ion chromatography. Some applications of this technique, standardized and adopted to meet the requirements of Gharda Chemicals (which is a leading producer of agrochemicals in India), will be presented in this communication. These include analysis of the finished products [(a) dicamba dimethylamine (DMA)/potassium/sodium salt acid and (b) 2,4-dichlorophenoxyacetic acid (2,4-D)], and the process intermediates [(c) tetrachlorobutyric acid and (d) glyoxylic acid/glycollic acid/formic acid]. Ion chromatographic analysis of sub-ppm levels of 2,5-dibromo- and monochlorobromo-phenols, in 2,5-dichlorophenol, after adequate sample preparation steps, is also being presented.