Semihydrodynamic Injection for High Salt Stacking and Sweeping on Microchip Electrophoresis and Its Application for the Analysis of Estrogen and Estrogen Binding

Abstract

In this work, a semihydrodynamic (SHD) injection method was introduced and coupled with high salt stacking and electrokinetic chromatography for the analysis of estrogen and estrogen binding using a simple cross microchannel. The SHD method allows all samples to be hydrodynamically injected and focused into the separation channel at a relatively high flow rate and without splitting and diffusion, leading to reproducible bias-free injections of larger sample volumes (up to 50 nL) within 3 s. Moreover, the injection method is initiated without voltage switching, leading to a reduced mixing effect. Such advantages are well suited for performing stacking and sweeping on a microchip. We investigated the stacking effect under continuous and discontinuous co-ion conditions as well as under sweeping conditions. Micellar sweeping effect alone was relatively weak (7-8 times), partly due to a lower sodium cholate concentration (30 mM) used for the running buffer. By combining the sweeping effect with high salt stacking, however, up to a 200-300-fold enhancement factor could be achieved, and the high-salt and low-surfactant contents for the running buffer were favorable for binding study under nonequilibrium conditions. To the best of our knowledge, this is the first demonstration of the hydrodynamic injection used for high salt sample stacking on a microchip, also for further combining micellar electrochromatography and affinity separation for the analysis of hydrophobic ligand binding using microchip electrophoresis.

Pressure-actuated microfluidic devices for electrophoretic separation of pre-term birth biomarkers

“…Hydrodynamic injection has been used in the separation of model neurotransmitters,[19] and studies of hydrophobic ligand binding;[20] however, the sample was injected using off-chip pressure, and the microfluidic devices lacked the on-chip controls needed to automate sample movement. An on-chip pump and valve architecture can provide small volume control, improving analysis.…”

Thousand fold concentration of an alkaloid in capillary zone electrophoresis by micelle to solvent stacking

“…Over the last decades, hundreds of articles were published on on-line sample stacking in CE [3,4], including field amplified sample stacking [5][6][7][8][9][10], transient isotachophoresis (tr-ITP) [11][12][13], dynamic pH junction [14,15] and transient moving reaction boundary (tMCRBM) [16] as well as sample sweeping [17][18][19][20][21][22][23][24][25][26][27][28][29], etc. Each method relies on creating difference between the background electrolyte (BGE) or buffer solution zone and the sample zone or a special inserted zone for enrichment.…”

Instrumentation design for hydrodynamic sample injection in microchip electrophoresis: A review

“…Chen et al. performed stacking concentration and HD injection of estrogens into a glass ME. In this work, the EOF was used to focus the sample in the injection cross section of a chip during the loading.…”