Temperature on-line Concentration in Capillary Zone Electrophoresis: Experimental Conditions for the Concentration of Carboxylic Acids

MARCOS TASCÓN; LEONARDO G. GAGLIARDI; FERNANDO J. BENAVENTE MORENO

Budapest

Simposio; 36th International Symposium on High-Performance Liquid Phase Separations and Related Techniques (HPLC 2011 Budapest Symposium); 2011

Hungarian Society for Separation Sciences

<!-- @page { margin: 2cm } P { margin-bottom: 0.21cm } --> One of the major drawbacks of the reduced volumes required in microseparation techniques is their limited concentration sensitivity. There have been many attempts to overcome poor concentration limit of detection (LOD) in CE, without using off-line approaches. Developments aimed at improving ultraviolet, electrochemical, fluorescence, chemiluminiscent and mass spectrometry detection, have had limited success. Alternatively, several electrophoretic or chromatographic approaches for on-line preconcentration based on stacking or solid-phase extraction have been extensively investigated with excellent results. However, only a few researchers have realized about the potential of manipulating temperature, in combination or not with the previous strategies, for such purposes. Temperature has been extensively studied in CE, since temperature profile across the capillary column, which result from Joule heat, affect separation efficiency. However, a gradient of temperature could be also aid to establish an on-line preconcentration zone that later would be easily switched to separate the concentrated analyte. Using moderate temperature changes the chemical structure or space conformation could be not affected, raising a promising option even for analytes of limited thermal stability. However, there has been just a few attempts to use temperature to preconcentrate analytes before CE separation. At that time, results were poor and no further improvements were reported since then. On previous years, our research group have shown that proper experimental conditions allow temperature to drive the ionization degree of analytes and, consequently, their retention in liquid chromatography or migration in CE. In CE, temperature on-line preconcentration can be achieved in certain conditions if the partially ionized analyte at an appropriate temperature migrates with a certain effective electrophoretic mobility to the opposite direction of the electroosmotic flow. Theory indicates that there are no limits for analyte preconcentration. However, there are some experimental key aspects which result critical to obtain significant preconcentration factors. In this work, we detail the fundamentals and some of the keys aspects of temperature on-line preconcentration in CE investigating sensitivity enhancement for anions (carboxylic acids), which migrate towards the anode in fused silica capillary columns with cathodic EOF. J. C. Reijenga, L. G. Gagliardi, E. Kenndler, Journal of Chromatography A, 2007, 1155, 142–145. M.Mandaji, G. R. Bensam, R. B. Hoff, S. Hillebrand, E. Carrilho, T. L. Kist, Electrophoresis 2009, 30, 1501–1509 E. Hernandez, F. Benavente, V. Sanz-Nebot, J. Barbosa. Electrophoresis, 2008, 29, 3366–3376.