Microchip Electrophoresis of Oligosaccharides Using Large-Volume Sample Stacking with an Electroosmotic Flow Pump in a Single Channel

Abstract

The applicability of an online preconcentration technique, large-volume sample stacking with an electroosmotic flow pump (LVSEP), to microchip zone electrophoresis (MCZE) for the analysis of oligosaccharides was investigated. Since the sample stacking and separation proceeded continuously without polarity switching in LVSEP, a single "straight" channel microchip could be employed. In the MCZE analysis of oligosaccharides, sample adsorption onto the channel surface should be suppressed, so the straight microchannel was modified with poly(vinyl alcohol) (PVA). So far, the mechanism of LVSEP in the polymer-coated capillary or microchannel has not been reported, and thus, the LVSEP process in the PVA-coated channel was investigated by fluorescence imaging. Although it is well-known that the PVA coating can suppress the electroosmotic flow (EOF), an enhanced EOF with a mobility of 4.4 x 10(-4) cm(2)/(V x s) was observed in a low ionic strength sample solution. It was revealed that such temporarily enhanced EOF in the sample zone worked as the driving force to remove the sample matrix in LVSEP. To evaluate the analytical performance of LVSEP-MCZE, oligosaccharides were analyzed in the PVA-coated straight channel. As a result, both the glucose ladder and oligosaccharides obtained from bovine ribonuclease B were well enriched and separated with up to 2200-2900-fold sensitivity enhancement compared to those in a conventional MCZE analysis. The run-to-run repeatabilities of the migration time and peak height were good with relative standard deviations of 1.1% and 7.2%, respectively, which were better than those of normal MCZE. By applying the LVSEP technique to MCZE, a complicated voltage program for fluidic control could be simplified from four channels for two steps to two channels for one step.

On-line Sample Preconcentration by Large-volume Sample Stacking with an Electroosmotic Flow Pump (LVSEP) in Microscale Electrophoresis

“…41 In LVSEP-MCE, only a sample injection throughout a "single" straight channel and application of a constant voltage between both ends of the single channel are required, simplifying the experimental procedure and improving the detection sensitivity in MCE. Of course, the analysis time is dramatically reduced in MCE compared to conventional CE.…”

Recent Studies on Online Sample Preconcentration Methods inCapillary Electrophoresis Coupled with Mass Spectrometry

“…To achieve truly practical analysis, thus, smart construction of whole analytical system including sample collection and pretreatment is of more importance. For example, LVSS provides high sensitivity and resolution via a simple procedure (full-capillary injection and constant voltage application) [35][36][37][38][39][40], where the optimization process can be minimized. It is suitable for the total system development and therefore, further deeper understanding of OSP methods are required.…”

“…After the sample concentration, the focused analytes are separated by CZE in the BGE. As only tens-fold sensitivity increase is usually available due to limited injection volume, similar techniques such as field-amplified sample injection (FASI) and large-volume sample stacking (LVSS) have been developed to increase the loadable volume [35][36][37][38][39][40].…”

Effect of a Low-conductivity Zone on Field-amplified Sample Stacking in Microchip Micellar Electrokinetic Chromatography

“…The detailed mechanism of the reversal was not reported in previous papers, 30,31 but it is supposed that the extremely low ionic strength of the deionized water and the sample zones generate a temporary enhanced cathodic EOF. 35 Hence, it was suggested that the ionic strength of the low-C zone is not small enough to generate the temporary enhanced EOF, of which the velocity was faster than electrophoretic migration of the anionic micelle. Consequently, it is clarified that the low-C zone can be formed in the separation channels by migration of the anionic species in order to keep electroneutrality principle.…”