Instrumental Methods for Electrosorptive Detection in Liquid Chromatography

Techniques and instrumentation have been developed for the electrosorptive detection of selected anions at mercury and silver in ion chromatography and of surface-active organic substances at mercury. Detection based on differential double-layer capacitance has proven most generally useful, although pulse-based methods are also beneficial, especially at silver where they have special utility in countering adsorption effects. An ancillary, and more specialized technique developed for the determination of ions senses adsorption indirectly, relying on the kinetic facilitation imparted the rate of electroreduction of a transition-metal reactant by an adsorbed species. A less generally useful, but nevertheless complementary scheme based on the “tensammetric” peak may also be employed for the determination of organic species. A novel approach investigated for application to both ionic and neutral species is based on changes in the drop time of mercury caused by adsorption-induced changes in surface tension at the mercury/aqueous interface. Finally, more elaborate, “hyphenated” techniques - capacitive/capacitive and capacitive/amperometric detection - have also been developed for application to selected ions.