Effect of Methanol and Polymer Additives on Large-Volume Dual Preconcentration by Isotachophoresis and Stacking (LDIS) in Straight-Microchannels

In our previous study, we found that the combination of large-volume sample stacking with an electroosmotic flow pump (LVSEP) and transient isotachophoresis (tITP), which named large volume dual preconcentration by isotachophoresis and stacking (LDIS), was successfully applied to microchip electrophoresis (MCE). In MCE-LDIS, highly viscous background electrolytes (BGEs) containing sieving polymers such as hydroxypropyl(methyl cellulose) (HPMC) could be employed, which should be effective for concentrating and separating especially for bio-polymeric compounds such as proteins and glycans. To adjust both enrichment efficiencies and resolutions in MCE-LDIS, in this study, the effects of methanol and HPMC additives in the BGE were investigated. In the BGE containing no HPMC, the peak height of a standard dye was increased upon increasing the methanol contents from 0 to 20%, while from 20 to 60% that gradually became smaller. Since the viscosity of water was increased by the addition of 20% methanol from 1.0 to 1.6 cP, the band broadening of the focused analytes would be suppressed, improving the sensitivity enhancement factor (SEF) from 1550 to 8250. Furthermore, the use of the BGE containing both 10% methanol and 1.5% HPMC in LDIS gave the best SEF of 18300 for the standard dye. Addition of methanol and HPMC was also effective for the separation of oligosaccharides, improving the resolutions from 0.85~1.25 to 1.56~1.73. It was revealed that, therefore, methanol and polymer additives were quite important factor for adjusting both SEFs and resolutions in MCE-LDIS.