Magnetic ionic liquid-based liquid-liquid microextraction followed by ultra-performance liquid chromatography coupled with triple-quadrupole tandem mass spectrometry for simultaneous determination of neurotransmitters in human cerebrospinal fluid and plasma

A LC-MS/MS method for the simultaneous determination of 6-cyanodopamine, 6-nitrodopamine, 6-nitrodopa, 6-nitroadrenaline and 6-bromodopamine in human plasma and its clinical application in patients with chronic kidney disease

The aim of this study was to develop a high-performance liquid chromatography-tandem mass spectrometry method for the determination of 6-cyanodopamine, 6-nitrodopamine, 6-nitrodopa, 6-nitroadrenaline and 6-bromodopamine in human plasma samples. Strata-X 33 μm solid-phase extraction cartridges were used for the extraction of the catecholamines from human plasma samples. The catecholamines were separated in a 150 × 3 mm Shim-pack GIST C18-AQ column with 3 μm particle size, placed in an oven at 40°C and perfused with 82% mobile phase A (acetonitrile-H2O; 90:10, v/v) + 0.4% acetic acid and 18% mobile phase B (deionized H2O) + 0.2% formic acid at a flow rate of 340 μl/min in isocratic mode. The injected volume was 4 μl and the run lasted 4 min. The method was linear from 0.1 to 20 ng/ml and the lower limit of quantification was 0.1 ng/ml for all analytes. The method was applied to evaluate the plasma levels of catecholamines in plasma of patients with chronic kidney disease and allowed the detection for the first time of circulating levels of the novel catecholamines 6-bromodopamine and 6-cyanodopamine.

Deep eutectic solvent-based ferrofluid for highly efficient preconcentration and determination of metronidazole by vortex-assisted liquid-phase microextraction under experimental design optimization

To determine metronidazole in water samples, we developed an environmentally friendly, efficient, and straightforward ferrofluid-based liquid-liquid microextraction sample pretreatment technique. It is coupled with a high-performance liquid chromatography-ultraviolet analytical technique known for its sensitivity, speed, and precision. The magnetic separation of metronidazole-containing ferrofluid from the matrix was effortlessly achieved through the application of an external magnetic field, eliminating the need for centrifugation. Response surface optimization was employed to systematically determine the key experimental parameters influencing extraction efficiency, including pH, NaCl concentration, ferrofluid volume, and vortex duration. With a low detection limit (0.116 ng mL-1), a broad linear range between 0.5 and 700 ng mL-1 was achieved at optimal conditions. Additionally, acceptable spiking recoveries (94.3-97.3 %) and RSD values (≤3.7 %) for intra- and inter-day precision were attained in water samples. In conclusion, the effectiveness of the vortex and ferrofluid combination, along with the convenience of collection and elimination of the need for centrifugation, bestows a highly valuable technique for determining metronidazole in water samples.