Cationic labeling of oligosaccharides for electrophoretic preconcentration and separation with contactless conductivity detection

Cationic derivatization of oligosaccharides by quaternary ammonium label was investigated for capillary electrophoretic separation with transient isotachophoretic preconcentration (t-ITP) as detected by capacitively coupled contactless conductivity detection (C4D). Dextran ladder, prepared by partial hydrolysis of dextran, isomaltotriose, maltopentaose and maltoheptaose were derivatized by reductive amination with (2-aminoethyl)trimethylammonium chloride. This label provides permanent positive charge potentially also useful for mass spectrometry ionization. Capillary electrophoresis (CE) separations of the oligosaccharides were tested in zone electrophoretic (CZE) and combined t-ITP/CZE modes. The transient isotachophoretic preconcentration was performed by injecting the sample solution complemented by ammonium acetate into the acetic acid background electrolyte. In this case the ammonium ions served as leading electrolyte followed by the sample zone and the background electrolyte of acetic acid acted as terminating electrolyte. The oligosaccharides were focused into narrow zones by ITP principles and during the course of migration through the separation capillary relaxed into zone electrophoretic separation mode. The separated ones were detected by C4D detector with detection limits in the nanomolar concentration range.