Monitoring the Electroosmotic Flow in Capillary Electrophoresis Using Contactless Conductivity Detection and Thermal Marks

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• 作者：Renata Mayumi Saito ; Carlos Antonio Neves ; Fernando Silva Lopes ; Lucas Blanes ; José ; Geraldo Alves Brito-Neto ; Claudimir Lucio do Lago
• 刊名：Analytical Chemistry
• 出版年：2007
• 出版时间：January 1, 2007
• 年：2007
• 卷：79
• 期：1
• 页码：215 - 223
• 全文大小：268K
• 年卷期：v.79,no.1(January 1, 2007)
• ISSN：1520-6882

文摘

The fundamental aspects and the capillary electrophoresisusage of thermal marks are presented. The so-calledthermal mark is a perturbation of the electrolyte concentration generated by a punctual heating of the capillarywhile the separation electric field is maintained. Theheating pulse is obtained by powering tungsten filamentsor surface mount device resistors with 5 V during a fewtens to hundreds of milliseconds. In the proposed model,the variation of the transport numbers with the risingtemperature leads to the formation of low- and high-concentration regions during the heating. After coolingdown, the initial mobilities of the species are restored andthese regions (the thermal mark) migrate chiefly due tothe electroosmotic flow (EOF). The mark may be recordedwith a conductivity detector as part of a usual electropherogram and be used to index the analyte peaks andthus compensate for variations of the EOF. In a favorablecase, 10 mmol/L KCl solution, the theory suggests thatthe error in the measurement of EOF mobility by thismean is only -6.5 × 10^-7 cm² V^-1 s^-1. The method wasapplied to the analysis of alkaline ions in egg white, andthe relative standard deviations of the corrected mobilitiesof these ions were smaller than 1%. This is a challengingmatrix, because albumin reduces the EOF to 20% of itsinitial value after 11 runs. The combination of thermalmark, electrolysis separated, and contactless conductivitydetection allowed the measurement of the EOF of a silicacapillary with unbuffered KCl solution with constant ionicstrength. The overall approach is advantageous, becauseone can easily control the chemical composition of thesolution in contact with the inner surface of the capillary.