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

Abstract

A technique has been developed to enhance analyte focusing for capillary electrophoresis for the analysis of physiological samples. High-ionic strength samples are titrated to low-ionic strength online using pH-mediated sample stacking in conjunction with a dynamic pH junction. This method concentrates analytes by reducing their electrophoretic mobility during field-amplification. Parameters responsible for enhanced focusing were investigated, and an enhanced pH-mediated stacking method was optimized for anionic nucleosides. The process results in ultra-narrow peak widths, for example, 0.28 s for thymidine with a 10-minute analysis time. Peak width and resolution with the enhanced stacking method were also compared to normal base stacking and electrokinetic injection. With this technique, mass-loading capacity can be increased without degradation in peak shape and resolution is dramatically improved.

Electrostacking online sample pre‐concentration capillary electrophoresis with amperometric detection for β2‐agonists in human urine

“…Since these methods were obviously time-consuming and tedious, on-column sample stacking methods have been developed for coupling with CE. As reported in some references, the on-column sample stacking methods such as pH-mediated sample stacking [15], on-column isotachophoresis [16,17], field-amplified [18], large-volume sample stacking [19] and electrostacking [20], have been applied to pre-concentrate the polar analytes which can be loaded into the capillary and improve the analytical sensitivity.…”

Acid‐induced transient isotachophoretic stacking of basic drugs in co‐electroosmotic flow capillary zone electrophoresis

“…LODs of r14 and r30 ng/mL were reported for TCA and b blocker drugs, respectively. Although acid stacking overcomes the difficulties associated with high-ionic-strength samples with an additional promise of minimal to no sample pre-treatment [25][26][27][28][29][30], the low concentration of target analytes found in real samples will require an offline sample concentration step. In fact, dedicated sample extraction strategies will always be used with analytical separation methods in order to analyse the levels of analytes in real samples.…”

“…Lunte and co-workers developed a stacking method termed pH-mediated base or acid stacking [25][26][27][28][29][30]. In acid stacking, a plug of acid is injected after the sample of basic analytes.…”

“…In acid stacking, a plug of acid is injected after the sample of basic analytes. The proposed mechanism of focusing was based on field amplification in the sample zone [29,30]. The amplification was caused by a low-conductivity zone that formed due to the neutralization of the hydronium ion from the acid plug and the BGE anion.…”

Advanced CE for chiral analysis of drugs, metabolites, and biomarkers in biological samples

“…Here are several examples: field-enhanced sample injection (FESI)1SWP ($million-fold increase in sensitivity) [215,216], FESI1tITP (3000-fold concentration) [217], SWP1DPJ (suitable for a mixture of neutral and weakly acidic/basic analytes) [218], large volume sample stacking (LVSS)1DPJ (preconcentration of weak electrolytes) [219], pH-mediated FESS1DPJ (sensitivity enhancement only for ionizable analytes) [220], tITP1DPJ (50-fold increase in sensitivity, nanomolar LODs) [221], LVSS1SWP (LODs up to 10 À10 mol/L) [122], a cation selective exhaustive injection1SWP (50-200 pg/mg LODs, 6-8 ppt LODs) [222,223]. In addition to these techniques, counter-flow gradient focusing [224] and electrocapture [225] can be considered as the techniques based on a combination of field-strength-and chemically induced changes in velocity offering new interesting possibilities in on-line sample preparation.…”