Monitoring the electroosmotic flow in capillary electrophoresis using contactless conductivity detection and thermal marks

ACS Publications
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Journal Article
Analytical Chemistry, 2007, 79 (1), pp. 215 - 223
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The fundamental aspects and the capillary electrophoresis usage of thermal marks are presented. The so-called thermal mark is a perturbation of the electrolyte concentration generated by a punctual heating of the capillary while the separation electric field is maintained. The heating pulse is obtained by powering tungsten filaments or surface mount device resistors with 5 V during a few tens to hundreds of milliseconds. In the proposed model, the variation of the transport numbers with the rising temperature leads to the formation of low- and highconcentration regions during the heating. After cooling down, the initial mobilities of the species are restored and these regions (the thermal mark) migrate chiefly due to the electroosmotic flow (EOF). The mark may be recorded with a conductivity detector as part of a usual electropherogram and be used to index the analyte peaks and thus compensate for variations of the EOF. In a favorable case, 10 mmol/L KCl solution, the theory suggests that the error in the measurement of EOF mobility by this mean is only -6.5 10-7 cm2 V-1 s-1. The method was applied to the analysis of alkaline ions in egg white, and the relative standard deviations of the corrected mobilities of these ions were smaller than 1%.
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