Sequential preconcentration by coupling of field amplified sample injection with pseudo isotachophoresis-acid stacking for analysis of alkaloids in capillary electrophoresis.

A novel on-column sequential preconcentration method based on the combination of field-amplified sample injection induced by acetonitrile and pseudo isotachophoresis (ITP)-acid stacking is developed for simply but efficiently concentrating alkaloid cations in a high-salt sample matrix in capillary electrophoresis. Acetonitrile (70%) added to a sample solution with a high-salt sample matrix not only induces field-amplified sample stacking by decreasing conductivity but also acts as a termination reagent in the succeeding pseudo ITP. After sample injection had been completed, a plug of H(+) was injected electrokinetically and a neutralization reaction between H(+) and tartrate from the buffer solution produced a low conductivity zone, in which the injected analyte cations were further concentrated. With the sequential preconcentration method, a 3 orders of magnitude detection sensitivity (1,400-fold) increase could be observed compared with the conventional electrokinetic injection method, without compromising separation efficiency and peak shape, and detection limits of 0.1 ng/mL for myosmine and 0.3 ng/mL for anabasine with the conditions selected were achieved. The calibration curves demonstrated good linearity in the concentration ranges 1.3-600 ng/mL for myosmine and 4.9-900 ng/mL for anabasine, respectively. The proposed method has been used to analyze successfully trace alkaloids in cigarette samples.