Bonded Polymethacrylate Stationary Phases for Open Tubular Liquid Chromatographic and Electrochromatographic Separations Zhixin Jessica Tan, Vincent T. Remcho Department of Chemistry, West Virginia Uni ersity, Morgantown, WV 26506-6045 Received 3 January 1997; accepted 4 February 1997 Abstract: Using a new procedure developed in our laboratory for the preparation of thick polymethacrylate films bonded in fused silica capillaries, crosslinked polymeric stationary phases were synthesized in situ in 25- m-i.d. capillaries. The effect of monomer and crosslinker concentrations on the resulting polymer film Ž . was studied by open tubular capillary electrokinetic chromatography OTCEC Ž . using p-hydroxy benzoates parabens as test solutes. Retention of analytes showed interesting trends versus monomer and crosslinker concentrations, exhibiting max- ima at certain combinations rather than a continuous increase in capacity factor with increasing concentration. Because the electroosmotic flow can arise from both exposed silica and polymer surfaces, the flow velocity did not exhibit an obvious trend versus monomer andor crosslinker concentration. Open tubular liquid Ž . chromatographic OTLC separations were also achieved using head pressure as the driving force for bulk flow, without employing a high-voltage power supply or micro LC pump. 1998 John Wiley & Sons, Inc. J Micro Sep 10: 99 105, 1998 Key words: open tubular liquid chromatography; electrokinetic chromatography; poly- methacrylate; bonded stationary phases INTRODUCTION According to chromatographic theory, the high- est separation efficiency and speed can be obtained Ž . with small inner diameter i.d. open tubular columns, owing to their favorable flow characteris- tics 1 . For many years the full exploration of open Ž . tubular liquid chromatography OTLC and open tubular capillary electrokinetic chromatography Ž . Ž. OTCEC was hindered by two factors: 1 the lack of detectors and injectors which would not add sig- nificant band broadening to the miniaturized chro- Ž. matographic system and 2 difficulties encountered with the immobilization of a uniform stationary phase layer on the inside surface of the capillary having sufficient sample capacity to avoid overload- ing. Development of sensitive on-column detection techniques and novel injection schemes, especially techniques used in capillary electrophoresis, has re- sulted in open tubular liquid chromatography sys- Vincent T. Remcho was a postdoctoral research associ- ate under the direction of Cal Giddings in the early 1990s. Correspondence to: V.T. Remcho Contract grant sponsor: National Science Foundation; contract grant number: NSF-EPSCoR tems which provide for minimal external band broadening 2 5 . The challenge now is to fabricate suitable columns. Several methods have been uti- lized to realize a retentive layer: static coating pro- cedures 5, 6 , creation of a porous structure inside the capillary 7, 8 , and chemical immobilization of a monolayer 9 or a polymeric stationary phase 2 5, 10 13 on the inner wall of the capillary. Described herein is a new procedure developed in our laboratory 12 for the preparation of poly- methacrylate films bonded inside narrow fused silica capillaries. This procedure relies on thermal initia- tion of polymerization, enabling the use of conven- tional polyimide jacketed capillaries in column preparation and affording greater control over the conditions for film synthesis. Previous studies on linear polymer films 12 showed that the electroos- motic flow velocity and capacity factor of solutes on the resulting columns are related to the initial con- centration of monomer. Studies on crosslinked poly- mer films are presented in this article. Open tubular capillary electrokinetic chro- Ž . matography OTCEC was used to evaluate the chromatographic performance of these columns. OTCEC can easily accommodate very small sample volumes and very low flow rates, obviating the need Ž. Ž . J. Microcolumn Separations , 10 1 99 105 1998 1998 John Wiley & Sons, Inc. 99 CCC 1040-768598010099-07