Applications of photopolymers in the development of capillary electrochromatography

Capillary Electrochromatography (CEC) is a hybrid of high performance liquid chromatography (HPLC) and capillary electrophoresis (CE). It has gained recognition as a promising separation method. It has advantages such as high separation efficiency, high selectivity, low solvent and sample consumption, and low operational costs.; The high efficiency of CEC is due to the fact that the solvent is transported through a porous structure by electroosmosis instead of by hydrostatic pressures. This feature allows a plug-like flow profile, which is independent of the size of micro channels that the solvent goes through. Small diameter stationary particles, therefore, can be used to achieve high separation efficiencies. 1.5-μm octyldecyl silica (ODS) particles were packed into capillaries for the study of amino acid separations. 20 natural occurring amino acids were successfully separated within 10 minutes.; Despite its many advantages, CEC is not widely used. One of the major problems is frit fabrication. Frits are porous plugs that retain the stationary phase inside the capillary column. Photopolymers was discovered to be an excellent option for frit construction. The preparation process was simplified significantly and frits made of photopolymers were reliable and reproducible. The chemistry of the frits can be tuned by changing the composition of porogens and ratio of monomers so that the hydrophobicity of the frits can be matched with that of the stationary phase. No bubble formation occurred in our running conditions using these frits.; Photopolymers used as frits in CEC make possible the fabrication of semi-preparative CEC columns. Large-bore (≥550-μm internal diameter) capillary columns were used to achieve relatively large sample injection without increasing the sample plug length. Using large-bore capillaries, high sample load may allow fraction collections, which can be used for further analysis, such as microsequencing or mass spectrometry analysis. This need has increased in the last few years especially because there are increasingly smaller quantities of biological macromolcules must be isolated and characterized. 550-μm inner diameter capillary columns packed with 1.5-μm ODS were successfully prepared using photopolymers as frits. The frits were easily fabricated in these large-bore capillaries and can withstand a pressure up to 4000 psi. No packing particles were observed to leak out the column. Large sample injection volumes as high as 1 μl were successfully achieved. A popular anti-cancer drug, taxol and its precursor baccatin III were separated when the sample injection was as high as 10μg. This performance leads us to believe that semi-preparative CEC has great potential, especially in the pharmaceutical field. Chiral stationary phases can be packed in these large-bore capillaries for drug analysis. Semi-preparative quantities of samples can be isolated after purification using much smaller amount of a high-cost stationary phase such as cyclodextran.