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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.

A simple and convenient mode--moving chemical reaction boundary method-capillary zone electrophoresis (MCRBM-CZE)--was designed for the enhancement of separating efficiency of CZE. In this mode, the transient MCRBM is used for the on-line pre-treatment of sample. By analyses of tryptophan (Trp) and phenylalanine (Phe) as an example, the experiments by MCRBM-CZE were carried out and further compared with those by normal CZE without the transient MCRBM. The results reveal that by carefully selected appropriate electrolytes, a strong condensation effect can be achieved by using MCRBM-CZE; this effect can greatly improve the separation efficiency, resolution and peak height of Trp and Phe in CZE as compared with those of normal CZE of Trp and Phe. Even if the sample comprises high concentrations of salt, such as 80 mM NaCl (concentration of sodium ion up to 145.6 mM), the same condensation effect can also been observed; this implies obvious significance for biological samples like urine and serum. However, if the electrolytes was chosen inappropriately only a poor compression effect of sample was observed in the MCRBM-CZE runs.