Abstract
Over the past years, a great effort has been devoted to the development of new sorbents that can be used to pack or to coat extractive capillaries for in-tube solid-phase microextraction (IT-SPME). Many of those efforts have been focused on the preparation of capillaries for miniaturized liquid chromatography (LC) due to the reduced availability of capillary columns with appropriate dimensions for this kind of system. Moreover, many of the extractive capillaries that have been used for IT-SPME so far are segments of open columns from the gas chromatography (GC) field, but the phase nature and dimensions are very limited. In particular, polar compounds barely interact with stationary GC phases. Capillary GC columns may also be unsuitable when highly selective extractions are needed. In this work, we provide an overview of the extractive capillaries that have been specifically developed for capillary LC (capLC) and nano LC (nanoLC) to enhance the overall performance of the IT-SPME, the chromatographic separation, and the detection. Different monolithic polymers, such as silica C18 and C8 polymers, molecularly imprinted polymers (MIPs), polymers functionalized with antibodies, and polymers reinforced with different types of carbon nanotubes, metal, and metal oxide nanoparticles (including magnetic nanoparticles), and restricted access materials (RAMs) will be presented and critically discussed.
Highlights
Miniaturization in liquid chromatography (LC) has been a constant during the past decades, and nowadays, capillary LC (capLC) and nano LC (nanoLC) equipment is readily available under a variety of configurations [1].The main advantages of reducing the particle size and column diameter are the decrease on the consumption of both mobile and stationary phases, and a lower dispersion of the analytes on the column, which results in enhanced efficiency and mass sensitivity
A number of capillaries with sorbents of various chemical compositions have been proposed for complementing gas chromatography (GC) columns in order to improve the performance of in-tube solid-phase microextraction (IT-solid-phase microextraction (SPME)) coupled to capLC and nanoLC (Figure 1)
Most of those phases have been developed for nanoLC despite the fact that the number of IT-SPME-capLC methods is comparatively greater
Summary
Miniaturization in liquid chromatography (LC) has been a constant during the past decades, and nowadays, capLC and nanoLC equipment is readily available under a variety of configurations [1]. Unlike approaches that use column cartridges, IT-SPME may not be exhaustive if the volume the sample processed is high in comparison with the amount of extractive phase, but the required analyte detectability can be reached by increasing the sample volume passed through the capillary; water or the proper solvent can be passed through to the capillary after loading the sample, so that unwanted matrix compounds can be selectively flushed out. Less used, another possibility is to aspirate and dispense the sample through the capillary several times until a sufficient amount of the analytes is trapped (draw/eject IT-SPME). C18 (50 mm × 0.075 mm i.d., 3.5 μm) and HILIC
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