Microextraction columns for automated sample preparation. A review focusing on fully miniaturized column switching and bioanalytical applications

•Novelties in sorptive phases for online microextraction columns are reviewed.•Advances in particulate, monolithic, open-tubular, and fibrous extraction media.•The development of fully miniaturized column switching approaches is highlighted.•Focus on modern bioanalytical applications of fully miniaturized column-switching. Column switching (CS) emerged as a strategy for direct injection of raw biological samples and currently is the more versatile technique for the fully automated integration of the sample preparation and the chromatography analysis. At the miniaturized scale, CS addresses the matrix complexity and allows the injection of sample volumes larger than those supported by the capillary/nano analytical columns. Detectability can be significantly improved while preserving the analytical capillary/nano column and the proper functioning of the instrument. In the last two decades, fully miniaturized CS systems have been under continuous development. Innovative polymeric, inorganic, and nanomaterials-based extraction phases have been introduced and exploited in diverse column formats, including particle-packed, monolithic, fiber-packed, and open tubular, extraction media. This paper reviews the more recent advances in microextraction column technology for fully miniaturized column-switching systems. Modern sorptive phases and extraction will be described, discussing their potentialities, advantages, and limitations. The overview will emphasize the significance of those developments in bioanalytical applications. [Display omitted]