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The direct interface of microextraction technologies to mass spectrometry (MS) has unquestionably revolutionized the speed and efficacy at which complex matrices are analyzed. Solid Phase Micro Extraction-Transmission Mode (SPME-TM) is a technology conceived as an effective synergy between sample preparation and ambient ionization. Succinctly, the device consists of a mesh coated with polymeric particles that extracts analytes of interest present in a given sample matrix. This coated mesh acts as a transmission-mode substrate for Direct Analysis in Real Time (DART), allowing for rapid and efficient thermal desorption/ionization of analytes previously concentrated on the coating, and dramatically lowering the limits of detection attained by sole DART analysis. In this study, we present SPME-TM as a novel tool for the ultrafast enrichment of pesticides present in food and environmental matrices and their quantitative determination by MS via DART ionization. Limits of quantitation in the subnanogram per milliliter range can be attained, while total analysis time does not exceed 2 min per sample. In addition to target information obtained via tandem MS, retrospective studies of the same sample via high-resolution mass spectrometry (HRMS) were accomplished by thermally desorbing a different segment of the microextraction device.

On-site screening for target analytes in complex matrices, such as biofluids and food specimens, not only requires reliable and portable analytical instrumentation, but also solvent-free and easy-to-use sampling/sample preparation approaches that allow analytes of interest to be isolated from such matrices. The integration of sampling devices with field deployable instruments should be as efficient as possible, and should aim to provide rapid, precise, and accurate results that enable quick on-site decision. In this study, we evaluated solid-phase microextraction-transmission (SPME-TM) coupled to a portable single quadrupole MS system, via direct analysis in real time (DART), as an effective tool for the rapid screening of target analytes in biological and food matrices. Limits of quantitation (LOQ) in the low parts-per-billion levels (≤50 ng mL) were attained for most of the investigated analytes with total analysis times under 2 min per sample. Furthermore, we explored the suitability of this technology for on-site rapid molecular profiling of complex matrices. As a proof-of-concept, we demonstrate the rapid identification of milk samples from assorted animal and vegetal sources.

In this work, a new generation of solid-phase microextraction (SPME) coatings based on polytetrafluoroethylene amorphous fluoroplastics (PTFE AF 2400) as a particle binder is presented. The developed coating was tested for thermal and solvent-assisted desorption, demonstrating its compatibility with both gas- and liquid-chromatographic platforms. The incorporation of hydrophilic-lipophilic balance (HLB) adsorptive particles provided optimal extraction coverage for analytes bearing a broad range of hydrophobicities and molecular weights and of varied chemical diversity. The performance of the newly developed coating was compared to already established coatings based on different polymers such as divinylbenzene/carboxen/polydimethylsiloxane (DVB/Car/PDMS) and octadecyl/benzenesulfonic acid/polyacrylonitrile (C18/SCX/PAN) in order to assess the new prototype versus the existing technology. As this is the first documented instance of PTFE AF being used as a particle immobilizer for SPME, an assessment of the analyte uptake rate and extraction capability of the developed coating was carried out in comparison to other conventionally used polymers. Moreover, the new SPME probes were used to validate an analytical method for determination of banned doping substances, achieving limits of quantitation below the minimum required performance limits (MRPLs) set by the World Anti-Doping Agency (WADA) for most compounds. Considering the broad coverage of the coating in terms of analytes extracted and its suitability for both thermal- and solvent-assisted desorption, these new SPME probes will properly suit various metabolomics applications that involve the use of both gas- and liquid-chromatography.

This work aims to investigate the behavior of analytes in complex mixtures and matrixes with the use of solid-phase microextraction (SPME). Various factors that influence analyte uptake such as coating chemistry, extraction mode, the physicochemical properties of analytes, and matrix complexity were considered. At first, an aqueous system containing analytes bearing different hydrophobicities, molecular weights, and chemical functionalities was investigated by using commercially available liquid and solid porous coatings. The differences in the mass transfer mechanisms resulted in a more pronounced occurrence of coating saturation in headspace mode. Contrariwise, direct immersion extraction minimizes the occurrence of artifacts related to coating saturation and provides enhanced extraction of polar compounds. In addition, matrix-compatible PDMS-modified solid coatings, characterized by a new morphology that avoids coating fouling, were compared to their nonmodified analogues. The obtained results indicate that PDMS-modified coatings reduce artifacts associated with coating saturation, even in headspace mode. This factor, coupled to their matrix compatibility, make the use of direct SPME very practical as a quantification approach and the best choice for metabolomics studies where wide coverage is intended. To further understand the influence on analyte uptake on a system where additional interactions occur due to matrix components, ex vivo and in vivo sampling conditions were simulated using a starch matrix model, with the aim of mimicking plant-derived materials. Our results corroborate the fact that matrix handling can affect analyte/matrix equilibria, with consequent release of high concentrations of previously bound hydrophobic compounds, potentially leading to coating saturation. Direct immersion SPME limited the occurrence of the artifacts, which confirms the suitability of SPME for in vivo applications. These findings shed light into the implementation of in vivo SPME strategies in quantitative metabolomics studies of complex plant-based systems.

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