Peak broadening in microchip electrophoresis: A discussion of the theoretical background

Gaš, Bohuslav; Kenndler, Ernst

doi:10.1002/elps.200290003

Cited by 38 publications

(19 citation statements)

References 63 publications

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“…They are caused from longitudinal diffusion of the solutes, from the difference of analyte and co-ion mobility of the background electrolyte (electromigration dispersion), from adsorption of the analytes, from laminar flow, from coiling of the capillary, from thermal effects arising due to Joule heating of the solution. All dispersion effects have been described theoretically (see, e.g., recent reviews [1,2]), and the influence and relevance of the many parameters that determine the separation efficiency are well understood.…”

Section: Introductionmentioning

confidence: 99%

Influence of solvent on temperature and thermal peak broadening in capillary zone electrophoresis

et al. 2003

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The present paper deals with the role of the solvent on thermal peak broadening. One main solvent property that determines the magnitude of the temperature gradient due to the generation of Joule heat in capillary zone electrophoresis is the thermal conductivity. As organic solvents have lower thermal conductivity than water (methanol and acetonitrile, e.g., nearly by a factor of 3) it can be hypothesized that the temperature gradient inside the capillary is more pronounced in organic solvents compared to an aqueous solution. On the other hand, the temperature dependence of the ion mobility (which is responsible for the velocity profile and thus for thermal peak broadening) is smaller in organic solvents. To get insight into the thermal effect of the solvent, first the temperature of a solution in a cylindrical tube was calculated utilizing the heat balance equation. It was shown that the two theoretical models most common in the literature (based on the analytical solution or on an assumption of the parabolic temperature profile in the tube, respectively) give the same results. The latter model was chosen for the further calculations, adding a quadratic term to express the electric conductivity as a function of the temperature. The temperature at the inner capillary wall and center as function of the capillary dimensions and the electric power was computed for electrolytes with a given conductivity at 25.0 degrees C with water, methanol, and acetonitrile as solvents. Capillary cooling systems used were circulating liquid cooling, enforced air-cooling, and natural convection in still air. The mean temperature (averaged over the cross section) resulting from Joule heating was compared with experimentally determined temperatures established upon application of an electric field; the latter temperature was derived from the measurement of the electric conductance of the background electrolyte solution and its (measured) temperature dependence. All investigations were carried out with solutions of the same initial electric conductivity (about 0.5 S.m(-1) at 25.0 degrees C). Agreement is found for natural convection conditions, and the deviation between theoretical and experimental results for the forced air and circulated liquid cooling systems can be related to the poorly defined thermal conditions of the capillaries in commercial instrumentation (with a part in a thermostated cassette and a part outside). For given conditions the temperature gradients in the organic solvents exceed largely those in water, independent of the type of cooling. As a consequence, the thermal plate height is significantly larger in organic solvents, at least under conditions where the deviation from the Nernst-Einstein limiting case is not too high. However, even for the maximum applicable field strengths the thermal plate height contributions are negligible compared to longitudinal diffusion in all solvents.

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Section: Introductionmentioning

confidence: 99%

Influence of solvent on temperature and thermal peak broadening in capillary zone electrophoresis

et al. 2003

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“…The reason is a mismatch of the mobility of the analyte ion and that of the co-ion in the BGE. However, this is an oversimplification as demonstrated in the works of the groups of Beckers, Boč ek, Gaš , Poppe, and Vigh (see, e.g., reviews [35][36][37][38] dealing with such dispersion phenomena). An approximation for the plate height due to electromigration dispersion was described by Xu et al [39]:…”

Section: Peak-broadening Due To Electromigration Dispersionmentioning

confidence: 99%

Are the asserted advantages of organic solvents in capillary electrophoresis real? A critical discussion

Porras

Kenndler

2005

Electrophoresis

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Are the asserted advantages of organic solvents in capillary electrophoresis real? A critical discussionBackground electrolytes (BGEs) prepared in pure organic solvents are common alternatives to aqueous BGEs in capillary electrophoresis. Several general advantages of organic solvents over water have been asserted in the literature, namely (i) organic solvents increase the separation selectivity; (ii) organic solvents increase the separation efficiency; (iii) high separation voltages and/or high BGE ionic strengths can be used in organic solvents due to lower electric current compared to water. Related assumptions are that (iv) due to higher field strengths applicable in organic solvents the analysis time is shorter than in aqueous BGEs, and (v) the solubility and/or stability of components (either analytes or BGE chemicals) is higher/better in organic solvents. In the present work, these asserted advantages were critically evaluated based on the physical principles of ion transport and zone dispersion in solution. The result was that many of the above-mentioned general advantages are overestimated or even inexistent; often they have no fundamental basis.

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“…Thus, the lower bound for the theoretical plate height is h ideal = 2D/u m , where u m = L/t is the migration velocity of the species. In practice, however, there are various sources of band broadening that could contribute to s 2 in CZE [1][2][3]. One such source is the Joule heating effect caused by an electric current passing through the buffer solution [4][5][6][7][8][9].…”

Section: Introductionmentioning

confidence: 97%

“…The theoretical plate numbers (solid line), N = L det /(H T 1 H dif ), were calculated with the analytical model presented above without accounting for the contributions to theoretical plate height from injection, detection, and adsorption, etc. [1][2][3]. The dashed line represents the calculated plate…”

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Band-broadening in capillary zone electrophoresis with axial temperature gradients

Xuan

2005

Electrophoresis

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It is widely accepted that Joule heating effects yield radial temperature gradients in capillary zone electrophoresis (CZE). The resultant parabolic profile of electrophoretic velocity of analyte molecules is believed to increase the band-broadening via Taylor-Aris dispersion. This typically insignificant contribution, however, cannot explain the decrease in separation efficiency at high electric fields. We show that the additional band-broadening due to axial temperature gradients may provide the answer. These axial temperature variations result from the change of heat transfer condition along the capillary, which is often present in CZE with thermostating. In this case, the electric field becomes nonuniform due to the temperature dependence of fluid conductivity, and hence the induced pressure gradient is brought about to meet the mass continuity. This modification of the electroosmotic flow pattern can cause significant band-broadening. An analytical model is developed to predict the band-broadening in CZE with axial temperature gradients in terms of the theoretical plate height. We find that the resultant thermal plate height can be very high and even comparable to that due to molecular diffusion. This thermal plate height is much higher than that due to radial temperature gradients alone. The analytical model explains successfully the phenomena observed in previous experiments.

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Peak broadening in microchip electrophoresis: A discussion of the theoretical background

Cited by 38 publications

References 63 publications

Influence of solvent on temperature and thermal peak broadening in capillary zone electrophoresis

Influence of solvent on temperature and thermal peak broadening in capillary zone electrophoresis

Are the asserted advantages of organic solvents in capillary electrophoresis real? A critical discussion

Band-broadening in capillary zone electrophoresis with axial temperature gradients

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