Indirect Detection Methods in Capillary Electrophoresis

Abstract

An overview is given of existing indirect detection methods of inorganic and organic anions in capillary zone electrophoresis (CZE). Kohlrausch's regulating function (KRF), used by several researchers to predict the detection sensitivity of ultraviolet (UV)‐inactive analytes in CZE, is reviewed. Sensitive indirect photometric detection (IPD) of ionic compounds in CZE is largely governed by the value of the change in absorbance in a solute zone. This in turn depends on a transfer ratio (TR), ratio of the charge, and ratio of the electrophoretic mobility of the analyte and IPD reagent. The influence of other experimental parameters, such as pH, type and concentration of the absorbing electrolyte, detection wavelength, and absorption pathlength, on detection sensitivity are also critically discussed. An extensive part of this review deals with the separation of various classes ofionic analytes using capillary zone electrophoresis/indirect photometric detection (CZE/IPD). Different approaches for simultaneous separation and indirect detection of nonabsorbing anions and cations are evaluated. From this evaluation, some rules of thumb as to when these approaches will be most effective are drawn. In addition, indirect fluorescence detection (IFD) in CZE and micellar electrokinetic chromatography (MEKC) are reviewed and possible application areas are highlighted. Some recent developments in other indirect detection modes, such as indirect chemiluminescence detection (ICLD) and indirect conductivity detection (ICD), are outlined.