On-line isotachophoretic sample focusing for loadability enhancement in capillary electrochromatography-mass spectrometry

The use of isotachophoretic (ITP) sample focusing to improve the detection limits for the analysis of charged compounds in capillary electrochromatography (CEC) is described. A coupled-column set-up was used with a 220-mu m inner diameter capillary, in which counterflow TTP focusing was performed, connected via a T-junction to a 75-mu m inner diameter CEC capillary. As is illustrated, the use of ITP focusing resulted in a dramatic reduction of the sample concentration detection limits. To demonstrate the performance of the ITP-CEC combination, several cationic low-molecular mass compounds in a plasma and urine matrix an analysed using UV-absorbance and mass spectrometric detection. A linear calibration curve was constructed over three decades and detection limits in the low nmol/l range were found for academic samples, using UV-absorbance detection. (C) 2000 Elsevier Science B.V. All rights reserved.