Combination of large‐volume sample stacking with an electroosmotic flow pump with field‐amplified sample injection on cross‐channel chips

Abstract

A combination of two online sample concentration techniques, large‐volume sample stacking with an electroosmotic flow (EOF) pump (LVSEP) and field‐amplified sample injection (FASI), was investigated in microchip electrophoresis (MCE) to achieve highly sensitive analysis. By applying reversed‐polarity voltages on a cross‐channel microchip, anionic analytes injected throughout a microchannel were first concentrated on the basis of LVSEP, followed by the electrokinetic stacking injection of the analytes from a sample reservoir by the FASI mechanism. As well as the voltage application, a pressure was also applied to the sample reservoir in LVSEP‐FASI. The applied pressure generated a counter‐flow against the EOF to reduce the migration velocity of the stacked analytes, especially around the cross section of the microchannel, which facilitated the FASI concentration. At the hydrodynamic pressure of 15 Pa, 4520‐fold sensitivity increase was obtained in the LVSEP‐FASI analysis of a standard dye, which was 33‐times higher than that obtained with a normal LVSEP. Furthermore, the use of the sharper channel was effective for enhancing the sensitivity, e.g., 29 100‐fold sensitivity increase was achieved with the 75‐μm wide channel. The developed method was applied to the chiral analysis of amino acids in MCE, resulting in the sensitivity enhancement factor of 2920 for the separated d‐leucine.

Recent progress of sample stacking in capillary electrophoresis (2016–2018)

“…The combination of two online sample concentration techniques, LVSS with an EOF pump and FASI, in cross‐channel microchip electrophoresis was described by Kitagawa et al. . Anionic analytes (standard dye fluorescein) injected through a microchannel were first concentrated by LVSS, followed by FASI injection of the analytes.…”

Highly Sensitive Analysis in Capillary Electrophoresis Using Large-volume Sample Stacking with an Electroosmotic Flow Pump Combined with Field-amplified Sample Injection

“…[1][2][3][4][5][6][7][8] In our research group, on-line sample preconcentration by large-volume sample stacking with an electroosmotic flow pump (LVSEP) was applied to CE and microchip electrophoresis (MCE). [9][10][11][12][13][14][15][16] LVSEP experiments can be performed with simple procedures, i.e., the whole capillary sample-injection and the application of a voltage without polarity switching. Furthermore, the enriched analytes zone is moved to the capillary inlet, and its migration direction is automatically reversed toward the outlet, which gives both high sensitivity and almost no-loss of resolution.…”

LVSEP Analysis of Cationic Analytes in Non-Aqueous Capillary Electrophoresis

“…To improve the sensitivity, several on-line sample preconcentration techniques have been applied to NACE. Among various on-line sample preconcentration techniques in CE [5][6][7][8][9][10][11][12], large-volume sample stacking with an electroosmotic flow pump (LVSEP) has unique characteristics including efficient enrichments by a whole capillary sample-injection, simple experimental procedures based on a voltage application without polarity switching, and high resolutions according to the movement of the stacked analytes zone from the capillary inlet to the outlet [12][13][14][15][16][17][18][19][20]. In this study, LVSEP was combined with NACE to achieve highly sensitive analyses of cationic compounds with unique selectivities in non-aqueous media.…”