Spin-label electron paramagnetic resonance (SL-EPR) spectroscopy has become a powerful and useful tool for studying structure and dynamics of biomacromolecules. However, utilizing these methods at physiological temperatures for in-cell studies is hampered by reduction of the nitroxide spin labels and thus short half-lives in the cellular environment. Consequently, reduction kinetics of two structurally different nitroxides was investigated in cell extracts of Xenopus laevis oocytes using rapid-scan cw-experiments at X-band. The five member heterocyclic ring nitroxide PCA (3-carboxy-2,2,5,5-tetramethylpyrrolidinyl-1-oxy) under investigation features much higher stability against intracellular reduction than the six member ring analog TOAC (2,2,6,6-tetramethylpiperidine-N-oxyl-4-amino-4-carboxilic acid) and is therefore a suitable spin label type for in-cell EPR. The kinetic data can be described according to the Michaelis-Menten model and thus suggest an enzymatic or enzyme-mediated reduction process.

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Food can contain unwanted compounds and need to be analyzed for compounds like carcinogenic polycyclic aromatic hydrocarbons to ensure consumer safety. The analytes need to be extracted from the sample matrix and cleaned‐up to enable detection. However, established methods for clean‐up are labor intensive and have a high expenditure on organic solvents. Here, we show a newly developed micro‐solid‐phase extraction cartridge method to automate the clean‐up for analysis of polycyclic aromatic hydrocarbons in sunflower oil using gas chromatography with quadrupole‐orbitrap mass spectrometry with a TriPlus autosampler. This automated micro‐solid‐phase extraction cartridge method needs only 4 μL of vegetable oil sample and requires only 360 μL acetonitrile for elution, and, therefore, it needs only small amounts of organic solvent. Two different micro‐solid‐phase extraction cartridge methods were developed, one using two commercially available cartridges with florisil and octadecylsilane/Z‐Sep/CarbonX, and the other method using one commercially available cartridge with florisil followed by one self‐made cartridge with octadecylsilane/Z‐Sep. The latter method showed successful lipid removal and was further validated for 22 of 24 polycyclic aromatic hydrocarbon compounds in sunflower oil at a spiked level of 1090 μg/kg with recoveries ranging from 53 to 118% and relative standard deviation below 22%. This method shows promising short‐time clean‐up with low expenditure of solvents.

Animal feed is typically plant-based and can contain pesticide residues. Methods for testing food and feed samples, such as the Quick Easy Cheap Effective Rugged Safe (QuEChERS) method or the Swedish Ethyl Acetate (SweEt) method, successfully extract many pesticide residues. However, nonpolar pesticides, such as organochlorine pesticides, show poor recovery when extracted from lipid-rich samples. The previously developed water-acetonitrile-heptane-solid-phase-extraction (WAHSPE) method shows better recoveries for the nonpolar pesticides but requires two injections per sample and per instrument. Here, we present a modified version of the WAHSPE method for pesticides in fish feed using one injection per sample and per instrument. Of the 184 pesticides tested, 179 met the European Union Legislation’s validation criteria at a spike level of 50 μg/kg, showing recoveries between 70 and 120% and a relative standard deviation (RSD) below 20%. Organochlorine pesticides accounted for 14 of the tested compounds.

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