Capillary zone electrophoresis with on-line isotachophoretic sample pretreatment: Sample clean-up aspects

A theoretical model intended for characterizations of capillary zone electr ophoresis (CZE) separations of samples of unknown matrix compositions with on-line isotachophoresis (ITP) sample pretreatment was developed. Assuming the use of the column-coupling capillary electrophoresis (CE) separation sy stem, this model explicitly defines (i) potential sample interferents for a given CZE analyte in both stages of the ITP-CZE combination and (ii) resid ual sample interferents in the CZE stage, i.e., interfering sample constitu ents which cannot be removed from the sample by the ITP pretreatment using a particular combination of the ITP and CZE electrolyte systems. Relationsh ips applicable to estimations of sizes of these groups of sample interferen ts are provided by the model. A calculation procedure based on these relati onships was developed to test the model. The results from these tests obtai ned for a group of CZE analytes of different acid-base properties (p-sulfan ilic acid, hippuric acid, 2,6-dinitrophenol, and o-nitrophenol) show that a n effective use of the ITP-CZE combination in the column-coupling separatio n system requires (i) that the ITP and CZE electrolyte systems introduce di fferent separation mechanisms for the analyte and (ii) that the size of the sample fraction in which the analyte is transferred into the CZE column af ter the ITP pretreatment is kept at a minimum. Numerical data obtained in t hese tests for p-sulfanilic acid were in reasonable agreement with the ones provided by computer simulations of the CZE and ITP-CZE separations with t he sample matrix consisting of 264 anionically migrating constituents of kn own migration properties. (C) 1999 John Wiley & Sons, Inc.