SINTERED OCTADECYLSILICA AS MONOLITHIC COLUMN PACKING IN CAPILLARY ELECTROCHROMATOGRAPHY AND MICRO HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

Fused-silica capillaries were packed with porous 6-mu m octadecylated silica microspheres and subjected to thermal treatment in order to obt ain a column with porous silica based monolithic packing. After sinter ing, the monolithic packing was reoctadecylated in situ with dimethylo ctadecylchlorosilane. The mechanical strength and stability of the mon olithic column were significantly greater than those of conventional c olumns packed with particulate stationary phase. The performance of th e columns was evaluated in both mu-HPLC and capillary electrochromatog raphy (CEC) of small aromatic compounds and polycyclic aromatic hydroc arbons with 10 mM berate, pH 8.0, in acetonitrile-water mixtures as th e mobile phase. Since no untoward bubble formation was observed, CEC c ould be performed in a CZE unit without the need for pressurizing the monolithic column. The plate efficiency of the monolithic column was s imilar to that of columns freshly packed with the same particles and w as always higher in the CEC than in the mu-HPLC under otherwise identi cal conditions. The electrosmotic flow (EOF) velocity increased with t he acetonitrile content of the eluent in open fused-silica capillaries with octadecylated innerwall and in columns packed with sintered octa decylsilica. In contradistinction, the EOF velocity decreased with the organic strength of the eluent in raw fused-silica capillaries. The o pposite trend is attributed to the different effect of changing organi c modifier concentration on the accessibility of silanol groups at the raw and octadecylated silica surfaces. (C) 1998 Elsevier Science B.V.