Quantitative study on selective stacking of zwitterions in large‐volume sample matrix by moving reaction boundary in capillary electrophoresis

Abstract

The paper advanced the theoretical procedures for quantitative design on selective stacking of zwitterions in full capillary sample matrix by a cathodic-direction moving reaction boundary (MRB) in capillary electrophoresis (CE) under control of electroosmotic flow (EOF). With the procedures, we conducted the theoretical computations on the selective stacking of two test analytes of L-histidine (His) and L-tryptophan (Trp) by the MRB created with 30 mM pH 3.0 formic acid-NaOH buffer and 2-80 mM sodium formate. The results revealed the following three predictions. At first, the MRB cannot stack His and Trp plugs if less than 12.5 mM sodium formate is used to form the MRB and prepare the sample matrix. Second, the MRB can stack His and/or Trp sample plugs completely if higher than 50 mM sodium formate is chosen to form the MRB. Third, the MRB can only focus His plug completely, but stack Trp plug partially if 20-50 mM sodium formate is used; this implied the complete MRB-induced selective stacking to His rather than Trp. All the three predictions were quantitatively proved by the experiments. With great dilution of sample matrix and control of EOF, controllable, simultaneous and MRB-induced selective stacking and separation of zwitterions were achieved. The theoretical results hold evident significances to the quantitative design of selective stacking conditions and the increase of detection sensitivity of zwitterions in CE. In addition, the control of EOF by cetyltrimethylammonium bromide (CTAB) can evidently improve the stacking efficiency to both His and Trp.

Quantitative investigations on moving chelation boundary within a continuous EDTA‐based sample sweeping system in capillary electrophoresis

“…If strong chelation reactant pairs, such as EDTA and Cu(II), are chosen, assumption (i) can be easily achieved (see details in Section 4.2). The other assumptions have been widely used by numerous researchers 10–28.…”

“…Relying on the concept of MRB 12–18, the method of MRB‐induced stacking was developed for the improvement of resolution of CE 19 and determination sensitivity 20. Recently, the relevant theory of stacking was developed for the quantitative design of sample stacking 21 and the simultaneous stacking and separation of amphoteric substance 22. However, the developed theory 21, 22 cannot be directly used to illuminate the mechanism of stacking of metal ion in the EDTA‐based sweeping system 10, 11.…”

“…Recently, the relevant theory of stacking was developed for the quantitative design of sample stacking 21 and the simultaneous stacking and separation of amphoteric substance 22. However, the developed theory 21, 22 cannot be directly used to illuminate the mechanism of stacking of metal ion in the EDTA‐based sweeping system 10, 11.…”

Quantitative analysis of lovastatin in capsule of Chinese medicine Monascus by capillary zone electrophoresis with UV–vis detector

“…This work also shows that CE is a powerful technique to determine lovastatin in the complex extract of the drug and fermentation. With simple online sample stacking [14,15], the sensitivity of determination can reach at the degree of ng/mL [16]. Recently our laboratory is developing work to enhance the detection sensitivity of Lvt by the simple stacking method.…”

Quantitative analysis of pyoluteorin in anti-fungal fermentation liquor of Pseudomonas species by capillary zone electrophoresis with UV–vis detector

“…HPCE is one of the most powerful analytical and separative techniques [10][11][12]. With simple online sample stacking [13][14][15], its determination sensitivity can reach at the degree of ng/mL, even at the level of pg/mL [16] with a normal UV-vis detector. However, no electrophoretic method has been reported for the determination of Plt so far.…”