Mechanistic Study on Analyte Focusing by Dynamic pH Junction in Capillary Electrophoresis Using Computer Simulation

Abstract

Dynamic pH junction is an on-line preconcentration method in capillary electrophoresis (CE) based on electrokinetic focusing of weakly ionic analytes with in large sample volumes in a multisection electrolyte system. In this report, experiments and computer simulations were performed to gain a better insight of the analyte focusing mechanism when a dynamic pH junction was used. A computer program, SIMUL, was used to simulate the band-narrowing process of a group for phenol derivatives under optimized buffer conditions, which were compared with experimental results. Computer simulations revealed the formation of a sharp moving pH boundary within the sample zone causing efficient focusing of long plugs of weakly acidic analytes based on their pKa. These studies offered useful information for understanding the band-narrowing process by control of the depth and lifetime of the moving pH boundary as a function of analyte pKa, sample pH, and injection length. The change in pH of the sample within the capillary was also estimated by measuring the absorbances of an analyte at two different wave-lengths. Optimization of analyte focusing resulted in enhanced detection responses of about 60-450-fold in terms of peak heights for some phenol derivatives' relation to conventional injections. Dynamic pH junction represents a novel approach to control band dispersion (peak width) and selectivity (mobility) of specific analytes for high-resolution CE separations.

Electrokinetic supercharging for highly efficient peptide preconcentration in capillary zone electrophoresis

“…The first uses interaction between the analytes and a pseudostationary phase to induce the preconcentration, and the second is based on pH differences along the separation path [12][13][14][15][16][17][18][19]. Although a high sensitivity enhancement can be reached when one of the above-mentioned methods is integrated in CZE, even higher SEFs can be achieved when combining these techniques.…”

Enhanced pH‐mediated stacking of anions for CE incorporating a dynamic pH junction

“…A short plug of BGE, with a lower pH than the separation BGE, is injected hydrodynamically prior to sample injection. The lower-pH BGE ahead of the sample zone serves to reduce the electrophoretic mobility of the analytes by reducing the analyte charge state and creating a dynamic pH junction [ 3,[15][16][17]. Sample injection and subsequent hydroxide injection occur as previously described for normal base stacking.…”

Dynamic computer simulations of electrophoresis: A versatile research and teaching tool

“…This is similar to the enforced migration method examined by Mosher et al [139] discussed above, although in this case it is transient in nature and is destroyed prior to migration by ZE. Kim et al [204] and Lee et al [205] used SIMUL to simulate the formation and movement of a pH boundary and its influence on stacking weak acids and amino acids, respectively. The pH boundary eventually dissipates allowing stacked analytes to be separated according to their electrophoretic mobilities.…”