Optimizing Conditions to Generate Frits in Capillary Microcolumns

LEONARDO G. GAGLIARDI; CECILIA B. CASTELLS; SONIA KEUNCHKARIAN

Batimore

Simposio; ITP 2012-19th International Symposium, Exhibit & Workshops on Electro- and Liquid Phase-separation Techniques; 2012

<!-- @page { margin: 2cm } P { margin-bottom: 0.21cm; direction: ltr; color: #000000; text-align: left; widows: 0; orphans: 0 } P.western { font-family: "Liberation Serif", "Times New Roman"; font-size: 12pt; so-language: es-AR } P.cjk { font-family: "WenQuanYi Micro Hei"; font-size: 12pt; so-language: zh-CN } P.ctl { font-family: "Lohit Hindi"; font-size: 12pt; so-language: hi-IN } A:link { so-language: zxx } --> <!-- @page { margin: 2cm } P { margin-bottom: 0.21cm; direction: ltr; color: #000000; text-align: left; widows: 0; orphans: 0 } P.western { font-family: "Liberation Serif", "Times New Roman", serif; font-size: 12pt; so-language: es-AR } P.cjk { font-family: "WenQuanYi Micro Hei", "Arial Unicode MS"; font-size: 12pt; so-language: zh-CN } P.ctl { font-family: "Lohit Hindi"; font-size: 12pt; so-language: hi-IN } A.western:link { so-language: zxx } A.ctl:link { so-language: zxx } --> Since its first years Capillary Electrodriven Chromatography (CEC) has demonstrated to be a promising separation technique. The flat flow speed profiles and the virtually unlimited possibility to extend the column lengths leads to efficiencies in the order of 100 000 theoretical plates or higher, this is, 10-fold or more of the typical efficiencies obtained in HPLC. However, difficulties for the reproducible production of capillary columns constituted an important drawback that make HPLC techniques to lead the market of standard methods for the analytical separation of liquids. One of the most important source of non-reproducibility is the generation of the porous devices (frits) to retain the particle beds. Due to the ?micro? scale, porous devices must be generated in-situ and the control of the experimental conditions at these scales is naturally difficult. Porous devices based on silica particles have some advantages since it is the same material of the tube wall. They have excellent properties from both, the mechanical and chemical point of view. Procedures described on literature for sinterizing silica particles involve radial heating of the capillary tube with electric resistances. This leads to radial inhomogeneities across the frit, localized zones of strong electric fields heating and forming bubbles, differences in permeability, peak dispersion and loss of efficiency. Additionally, with these method it is difficult to control the frit length. In this work we introduce a method to obtain silica frits by frontal exposition of the extreme of capillary tubes filled with silica particles to a controlled source of heat (muffle oven). Experimental details and conditions, such as temperature, exposition time, introduction of particles, etc., have been optimized. SEM imaging, chromatographic and electrophoretic characterizations are also used to study the frits generated in the different conditions.