Column packing technology in capillary electrochromatography and capillary liquid chromatography

Capillary electrochromatography (CEC) is a rapidly emerging separation technique employing electroosmosis rather than pressure driven flows to drive the solvent and solutes through a capillary column. Although CEC is developing into a powerful technique in the arsenal of electroseparations, difficulties associated with the packing and fabrication of the chromatographic column have hindered the widespread use of CEC. To better understand and simplify column fabrication in CEC, we have examined two aspects of packed columns: (1) optimization of column packing protocols and frit fabrication, and (2) increasing column performance. First, we investigated the available packing protocols for fabricating packed CEC columns, namely columns packed by slurry pressure, supercritical CO₂, electrokinetic, and centripetal forces. Slurry pressure and centripetal forces were utilized previously in our laboratory. A lab-built electrokinetic packing apparatus was constructed and modifications to existing equipment were made to accommodate supercritical CO₂. Columns were fabricated with all the techniques demonstrating the feasibility of each, with results comparable to those found in the literature. Columns packed by centripetal forces and supercritical CO₂ performed superior to columns packed by the other techniques. In examining the various protocols, it became apparent to us that experience of the practitioner and familiarity with packing equipment were important factors in column fabrication, especially in the fabrication of the retaining frits. Upon further investigation of the packing techniques and optimization of our frit fabrication protocol, we observed similar performance in columns packed by all four techniques. Our optimized method of frit fabrication produced frits ∼1 mm in length in a simple and reproducible fashion. Additionally, we acquired columns packed by other laboratories proficient in electrokinetic and supercritical CO₂ packing techniques and demonstrated that columns packed in our laboratory using the same packing techniques performed similarly.; Second, we addressed the ability to increase column performance by incorporating a drying step in the packing protocol. Columns packed by centripetal forces were subjected to a drying step that yielded columns with increased efficiency and retention compared to columns not submitted to the drying step.{09}Columns packed by supercritical CO₂, a pseudo dry packing technique, showed increased separation efficiency in comparison to columns maintained under wet conditions. New column formats were also investigated as a means for increasing performance. Capillary columns of square geometry were evaluated for CEC and compared to cylindrical ones. Square and cylindrical columns both performed similarly, with the main advantage of the square columns being the increased detection signal-to-noise ratio.