Analytical potential of mesofluidic lab-on-a-valve as a front end to column-separation systems Manuel Miro ´, Hugo M. Oliveira, Marcela A. Segundo The lab-on-a-valve (LOV) integrated microdevice has recently attracted much attention as a functional mesofluidic platform for programmable, pressure-driven flow as compared to lab-on-a-chip counterparts. We review the current state of the art of LOV as a versatile front end to column-separation techniques, namely, liquid chromatography (LC), gas chromatography (GC) and capillary electrophoresis (CE) for automatic mesofluidic handling at the low-microliter level, in-line sample processing and introducing the appropriate form of the analyte into the instrument for separation or detection. The open architecture of the LOV monolith unit has been to date exploited to accommodate micro solid-phase extraction in a renewable fashion, the so-called bead-injection analysis, encompassing reversed-phase materials and molecularly imprinted polymers, and in-valve microscale affinity chromatography. A plethora of interfaces have been recently devised for reliable injection of minute, well-defined volumes of analyte-containing solutions into LC,GC or CE We illustrate these applications with representative examples in environmental and bioanalytical arenas. ª 2010 Elsevier Ltd. All rights reserved. Keywords: Lab-on-a-valve; Flow analysis; Bead-injection analysis; Capillary electrophoresis; Gas chromatography; Liquid chromatography; Mesofluidic; Micro affinity chromatography; Micro solid-phase extraction 1. Introduction Notwithstanding the fact that chroma- tography has been consolidated as a rou- tine and research tool for assays in a vast number of analytical fields, sample prep- aration is still the bottleneck for reliable and unbiased analysis. Multi-step con- ventional sample processing is the most error-prone part of the analytical process and accounts for some two-thirds of the overall time of liquid chromatographic (LC), gas chromatographic (GC) or capil- lary electrophoretic (EC) assays [1]. The continual quest for novel sample- preparation techniques has led to the development of faster, more cost-effective, miniaturized versions of sample extraction with green chemical credentials to replace conventional methods [1,2]. Liquid-phase microextraction (LPME) techniques, and variants thereof [i.e. single-drop LPME, dispersive LPME, solidified floating organic drop, and hollow-fiber assisted LPME] are gaining ground prior to column-separa- tion systems [3–5] over time-consuming, labor-intensive traditional liquid-liquid extraction (LLE) with the added advantage of reduced exposure of the analyst to harmful organic solvents. However, the predominant sample-processing methods that have been rapidly growing in recent years as a consequence of the improved enrichment factors, and, thus, sensitivity for chromatographic assays as compared to LLE and LPME, are solid-phase extrac- tion (SPE) and miniaturized versions thereof including fibre/needle-based solid- phase microextraction (SPME), in-tube capillary SPME, stir-bar sorptive extrac- tion (SBSE), and micro-solid phase extraction (lSPE) in the format of packed microcolumns, syringes or pipette tips [1,2,6,7]. Much effort has gone into the develop- ment of not merely miniaturized but also automated sample pre-treatment ap- proaches to simplify the overall analytical process, capitalizing on robotic systems (e.g., Prospekt, Prospekt-2 and Symbiosis from Spark Holland or OS-2 from Merck for lSPE prior to LC) [8] or flow-based approaches [9–11]. Automation of sample processing exploiting the first and second Manuel Miro ´* Department of Chemistry, Faculty of Sciences, University of the Balearic Islands, Carretera de Valldemossa km 7.5, E-07122 Palma de Mallorca, Illes Balears, Spain Hugo M. Oliveira, Marcela A. Segundo, REQUIMTE, Departamento de Quı ´mica, Faculdade de Farma ´cia, Universidade do Porto, Rua Anı ´bal Cunha, 164, 4099-030 Porto, Portugal * Corresponding author. Tel.: +34 971172746; Fax: +34 971173426; E-mail: manuel.miro@uib.es Trends in Analytical Chemistry, Vol. 30, No. 1, 2011 Trends 0165-9936/$ - see front matter ª 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.trac.2010.08.007 153