Peak Intensity in Ion-Exchange Chromatography with Bulk-Property Detectors

Abstract

Intensities of the analyte and the two kinds of system peaks in ion-exchange chromatography with bulk-property detectors, such as conductivity detector and UV absorbance detector in indirect mode, were investigated theoretically and experimentally. Extensive computer simulations of the chromatographic processes, not only for monobasic acid eluent systems but also for dibasic strong-acid eluent systems, were performed first. Then, the functional relationships between the peak intensity and chromatographic parameters (the acid dissociation constant, the eluent concentration, the eluent acidity, the acid-partition coefficient, etc.) were derived, and confirmed experimentally. The peak intensity variation previously observed for common anions with the Tiron eluent has been explained clearly. There are two kinds of sensitivity enhancement in conductivity detection when the retention volume of the 2nd system peak is larger than that of an analyte peak (k x ' <k 2 ' ). Both are caused by the acid partition phenomenon. One depends essentially on the chromatographic processes and becomes larger when k 2 ' is close to k x ' . The other is simply explained by the stoichiometric and equilibrium considerations on the chemical reactions in a column. These two kinds of enhancement are additive. With an acid eluent and conductivity detection, the intensity of analyte peaks is remarkably enhanced. This sensitivity increase is very useful in the practice of non-suppresser IC. Moreover, the first system peak is very small with acid eluents. This is advantageous for the detection of the species of low retention.