PubMed · 13148188
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D C TOPP. Paper electrophoretic separation.. https://pubmed.ncbi.nlm.nih.gov/13148188/
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Analyses of amino acids and peptides were performed using a quartz microchip and an interface for microchip electrophoresis-electrospray ionization mass spectrometry (MCE-ESI-MS). In MCE-ESI-MS, negative pressure caused by ESI increased band broadening and deteriorated separation. We tried to suppress the negative pressure and improve separation using a microchip with a long separation channel. Separations of peptide standards were compared using two microchips with long separation channel (58.9 mm) and short one (22.9 mm). Theoretical plate numbers and resolution were improved significantly using the former. The theoretical plate numbers of [Val4]angiotensin was 8600 using the former and 1700 using the latter. When background electrolytes of low pH were used in an uncoated quartz microchip, electrokinetic injection was difficult because of weak electroosmotic flow. The use of successive multiple ionic polymer layers coating of the microchip channel stabilized electrokinetic injection and permitted analysis of amino acids and peptides even under low pH conditions. Separation of amino acids was successfully performed using formic acid solution (pH 2.5) as background electrolyte.
An attempt is made to revisit the main theoretical considerations concerning temperature effects ("Joule heating") in electro-driven separation systems, in particular lab-on-a-chip systems. Measurements of efficiencies in microfabricated devices under different Joule heating conditions are evaluated and compared to both theoretical models and measurements performed on conventional capillary systems. The widely accepted notion that planar microdevices are less susceptible to Joule heating effects is largely confirmed. The heat dissipation from a nonthermostatically controlled glass microdevice was found to be comparable to that from a liquid-cooled-fused silica capillary. Using typically dimensioned glass and glass/silicon microdevices, the experimental results indicate that 5-10 times higher electric field strengths can be applied than on conventional capillaries, before detrimental effects on the separation efficiency occur. The main influence of Joule heating on efficiency is via the establishment of a radial temperature profile across the lumen of the capillary or channel. An overall temperature increase of the buffer solution has only little influence on the quality of the separation. Still, active temperature control (cooling, thermostatting) can help prevent boiling of the buffer and increase the reproducibility of the results.
This paper describes the development of an annular chamber designed for preparative free-flow electrophoresis which can operate at voltages up to 20 kV, electric fields up to 65 kV/m, and power densities as high as 10 MW/m(3). This apparatus uses counter-rotating fluid vortices to stabilize the aqueous medium in the annulus against natural convection while improving heat and mass transfer over vortex-free Couette flow. The vortices are generated by rotating the inner surface of the annulus and, if the rotor and stator have complementary shapes, dispersion induced by electrokinetic and electrohydrodynamic flows can be mitigated even at the highest operating voltages. Following a brief overview of contemporary annular free-flow instrumentation, the theoretical principles for momentum and heat transport in the vortices are discussed in some detail and then the results of several electrofocusing experiments are provided to illustrate the resolving power of this instrument.