Stacking ionizable analytes in a sample matrix with high salt by a transient moving chemical reaction boundary method...

The paper presents a novel on-line transient moving chemical reaction boundary method (tMCRBM) for simply but efficiently stacking ionizable analytes in high-salt matrix in capillary zone electrophoresis (CZE). The powerful function and stability of the tMCRBM are elucidated with the ionizable test analytes of L-phenylalanine (Phe) and L-tryptophan (Trp) in the matrix with 85.6-165.6 mM sodium ion and further compared with the normal CZE of Phe and Trp samples dissolved in running buffer. The results verify that (1) the on-line tMCRBM mode can evidently increase separation efficiency, peak height, and resolution, (2) with the mode, the analytes in a 28-cm high-salt matrix plug can be stacked successfully and further separated well, (3) the values of relative standard deviation of peak height, peak area, and migrating time range from 3.9% to 6.1%; the results indicate the high stability of the technique of tMCRBM-CZE. The techniques implies obvious potential significance for those ionizable analytes, e.g., protein, peptide, and weak alkaline or acidic compound, in such matrixes as serum, urine, seawater, and wastewater, with high salt, which has a deleterious effect on isotachophoresis (ITP) and especially on electrostacking and field-amplified sample injection (FASI). The mechanism of stacking of zwitterionic analytes in a high-salt matrix by the tMCRBM relies on non-steady-state isoelectric focusing (IEF) but not on transient ITP, electrostacking, and FASI.