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Liquid chromatography on columns with small internal diameters has been reviewed as the intermediate technique between conventional liquid chromatography and microchip separations. The development of micro column separations in the early years has been described, starting with the papers of Horváth and co-workers and Ishii and co-workers, continuing into the first part of the eighties, then making a leap in time to recent innovations with small-bore columns. Based on internal diameters a classification of the different analytical HPLC columns has been suggested. The advantages of small-bore columns have been discussed, with particular emphasis on the advantage of coupling to concentration sensitive detectors when the sample amount is limited. Open tubular columns are treated as a part of the historic background. The recent developments include a brief look into the current status of monolithic columns, the use of packed nano columns and micro columns with electrospray mass spectrometry, and the potential of two-dimensional comprehensive liquid chromatography. Finally, the coupling of sample preparation to analytical columns and the future applications of the novel technological improvements to the microchip separation methods have been discussed.

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Solid-phase microextraction (SPME) is a solvent-free sample preparation technique using a thin coating attached to the surface of a fused silica-fiber as the extraction medium, which has been successfully applied to the analysis of a wide variety of compounds by coupling to gas chromatography (GC). In recent years, in-tube SPME using GC capillary column as the extraction medium has also been developed and coupled with liquid chromatography (LC) for the preconcentration of nonvolatile compounds. In this study, an on-line interface between the fiber-in-tube SPME and capillary electrophoresis (CE) has been developed, and the preconcentration and separation of four tricyclic antidepressant (TCA) drugs, amitriptyline, imipramine, nortriptyline, and desipramine, were performed with the hyphenated system. Under the optimized condition, a better extraction performance than conventional in-tube SPME was obtained, even the length of the extraction medium was much shorter. The results clearly indicated that the fiber was working effectively as an extraction medium. For the separation of these four TCAs, capillary electrophoretic separation with beta-cyclodextrin as the buffer additive has been employed and the application of the developed system to the analysis of complex sample mixtures in a biological matrix is also demonstrated.

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