This study reports a fast, sensitive, and selective column switching ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method to determine the endocannabinoids (eCBs), anandamide (AEA), and 2-arachidonoylglycerol (2-AG) in plasma samples. This bidimensional system used a restricted access media column (RP-8 ADS, 25 mm × 4 mm × 25 μM) in the first dimension and a core-shell Kinetex C18 (100 mm × 2, 1.7 mm × 1 μM) column in the second dimension, followed by detection in a mass spectrometer triple quadrupole (multiple reactions monitoring mode) operating in the positive mode. RP-8 ADS was used for trace enrichment of eCBs (reverse phase partitioning) and macromolecular matrix size exclusion; the core-shell column was used for the chromatographic separation. The column switching UHPLC-MS/MS method presented a linear range spanning from 0.1 ng mL (LOQ) to 6 ng mL for AEA and from 0.04 ng mL (LOQ) to 10 ng mL for 2-AG. Excluding the LLOQ values, the precision assays provided coefficients of variation lower than 8% and accuracy with relative standard error values lower than 14%. Neither carryover nor matrix effects were detected. This high-throughput column switching method compared to conventional methods is time saving as it involves fewer steps, consumes less solvent, and presents lower LLOQ. The column switching UHPLC-MS/MS method was successfully applied to determine AEA and 2-AG in plasma samples obtained from Alzheimer's disease patients. Graphical abstract A column switching ultra high-performance liquid chromatography-tandem mass spectrometry method using RP-8 ADS column and core shell column to determine endocannabinoids in plasma samples.

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A reliable method was developed and validated based on dispersive liquid-liquid microextraction (DLLME) and ultra-high-performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS) to determine simultaneously methylparaben (MePB), ethylparaben (EtPB), propylparaben (PrPB), and butylparaben (BuPB) in breast milk samples. A central composite design 2 4 with four independent variables and five levels of variance was used to optimize the DLLME conditions. The DLLME/UHPLC-MS/MS method was linear from 5 (lower limit of quantification, LLOQ) to 100 ng mL -1 (upper limit of quantification, ULOQ). The inter-assay and intra-assay precision values presented coefficients of variation (CVs) lower than 15%, and the relative standard error of the inter-and intra-assay accuracy values was lower than 10.4%. The DLLME/UHPLC-MS/MS method was successfully applied to determine parabens in human milk samples obtained from sixteen volunteer lactating mothers.

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In-tube solid-phase microextraction with a capillary column as extraction device can be directly coupled with high-performance liquid chromatography systems (HPLC). The in-tube solid-phase microextraction technique has been continuously developed since it was introduced in 1997. New couplings have also been evaluated on the basis of state-of-the-art HPLC instruments. Different types of capillaries (wall-coated open tubular, porous layer open tubular, sorbent-packed, porous monolithic rods, or fiber-packed) with selective stationary phases (monoliths, magnetic nanoparticles, conducting polymers, restricted access materials, ionic liquids, carbon, deep eutectic solvents, and hybrid materials) have been developed to boost in-tube solid-phase microextraction performance (sorption capacity and selectivity). This technique has been successfully applied to analyze biological samples (serum, plasma, whole blood, hair, urine, milk, skin, and saliva) for therapeutic drug monitoring, to study biomarkers, to detect illicit drugs, to conduct metabolomics studies, and to assess exposure to drugs. This review describes current advances in in-tube solid-phase microextraction extraction devices and their application in bioanalysis. K E Y W O R D Sbioanalysis, capillary coatings, in-tube solid-phase microextraction, online systems INTRODUCTIONBioanalysis is a subdiscipline of analytical chemistry that quantitatively measures xenobiotics (chemically

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