Simultaneous Separation of Acidic, Basic, and Neutral Organic Compounds, Including Strong and Moderate Acids and Bases, by Capillary Electrochromatography

Abstract

The separation of strongly basic, moderately basic, weakly basic, strongly acidic, moderately acidic, weakly acidic, and neutral compounds in a single run using capillary electrochromatography (CEC) is presented. This is accomplished using a 3-μm CEC Hypersil C8 capillary with high organic content acetonitrile/phosphate (pH 2.5) mobile phases containing hexylamine. Fifteen basic, acidic, and neutral drugs of forensic interest are resolved using a step gradient. Strong and moderately basic drugs separate before t_o, apparently by a combination of free zone electrophoresis (CZE) and chromatographic phenomena. Weak bases separate after t_o, also by a combination of CZE and chromatographic processes. Due to large selectivity differences between CEC and CZE for bases, there is evidence that the stationary phase is playing a significant role in the separation of these solutes. The CEC approach presented offers unique selectivity, expanded peak capacity, and the ability to solubilize both hydrophilic and hydrophobic solutes in an injection solvent that is compatible with the chromatographic system.