Study of the electroosmotic flow as a means to propel the mobile phase in capillary electrochromatography in view of further miniaturization of capillary electrochromatography systems

Abstract

In this paper, we investigate the phenomenon of electroosmosis as a means to propel a mobile phase, in particular in view of an application in microfluidic systems, which are characterized by significantly smaller volumes of the reservoirs and the separation channels compared to conventional instrumentation. In the microfluidic chip, pH changes due to water electrolysis quickly showed an effect on the electroosmotic flow (EOF), which could be counteracted by either regularly exchanging or buffering the mobile phase. Surface treatment was of no effect in regard to EOF stabilization in empty channels but may have an influence in channels filled with a charged monolith. In fused-silica capillaries the EOF was generally found to decrease from 'naked' to surface-treated to monolith-filled capillaries. The EOF tended to be higher when an organic solvent (acetonitrile) was added to the mobile phase and could be further increased by substituting the water with equal amounts of methanol. In addition, the hydrostatic pressure exerted by the EOF was investigated. In a microfluidic chip with empty (cross-)channels such an effect could be responsible for a redirection of the flow. In capillaries partially filled with a noncharged (non-EOF-generating) monolith, a linear relationship could be established between the EOF created in the empty section of the capillary (apparent mobility) and the length of the monolith (backpressure). In capillaries partially filled with a charged (EOF-producing) monolith, flow inhomogeneities must be expected as a consequence of a superimposition of hydrodynamic pressure and EOF as mobile phase driving force.

Separation and quantitative analysis of coumarin compounds from Angelica dahurica (Fisch. ex Hoffm) Benth. et Hook. f by pressurized capillary electrochromatography

“…(1). The same as the previous experiment [42], increasing the acetonitrile content in the mobile phase increases both the theoretical plates and the speed of the EOF. These results show the importance of the organic modifier for the zeta potential and dielectric constant, which affect the EOF and the ionic migration through the column.…”

Pressure‐assisted capillary electrochromatography with electrospray ionization‐mass spectrometry based on silica‐based monolithic column for rapid analysis of narcotics

“…The CEC method possesses high separation efficiency due to the very flat flow profile, which is generated by the electroosmotically driven mobile phase. Depending on both assisted pressure and electric field, the pCEC separation efficiency is between that of CEC and HPLC [40][41][42]. When the electroosmotic flow is predominantly responsible for driving the flow of mobile phase, high separation efficiency could be obtained.…”

Review on the development of truly portable andin-situcapillary electrophoresis systems

“…Unlike CE systems, CEC is able to separate out neutral solutes. Szekely et al [40] discussed the difficulty of maintaining a stable EOF, in their miniaturized CEC system due to pH changes; a consequence of electrolysis in the small buffer reservoirs inherent in many microfluidic systems. They measured moderate changes in the pH of buffered solutions following the application of a high voltage to the reservoirs.…”