[Simultaneous determination of seven quaternary ammonium compounds in frozen food by ultra performance liquid chromatography-tandem mass spectrometry combined with modified QuEChERS method].

Quaternary ammonium compounds (QACs) are a class of cationic surfactants that can be used as the main active ingredient of disinfectants. The increased use of QACs is concerning as exposure from inhalation or ingestion to these compounds that has been associated with adverse effects on the reproductive and respiratory systems. Humans are exposed to QACs primarily by food consumption and inhalation of air. QAC residues pose significant threats to public health. Given the importance of assessing potential residue levels for QACs in food, therefore, a method was developed for the simultaneous detection of six common QACs and one emerging QAC (Ephemora) in frozen food by ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) coupled with the modified QuEChERS method. The main factors governing the response, recovery, and sensitivity of the method, including extraction solvents, types and dosages of adsorbents, apparatus conditions, and mobile phases, were optimized in the course of sample pretreatment and instrument analysis. QAC residues in frozen food were extracted using 20 mL methanol-water (90∶10, containing 0.5% formic acid) for 20 min by the vortex shock method. The mixture was ultrasonicated for 10 min and centrifuged at 10000 r/min for 10 min. A 1-mL aliquot of the supernatant was transferred to a new tube and purified using 100 mg of PSA adsorbents. After mixing and centrifugation at 10000 r/min for 5 min, the purified solution was analyzed. Target analytes were separated on an ACQUITY UPLC BEH C8 chromatographic column (50 mm×2.1 mm, 1.7 µm) at a column temperature of 40 ℃ and a flow rate of 0.3 mL/min. The injection volume was 1 µL. Gradient elution was performed using methanol and 5 mmol/L ammonium acetate solution as the mobile phases. Multiple reaction monitoring (MRM) was conducted in the positive electrospray ionization (ESI+) mode. The matrix-matched external standard method was used to quantify seven QACs. The optimized chromatography-based method completely separated the seven analytes. Good linear relationships were obtained for the seven QACs in the range of 0.1-100.0 ng/mL. The correlation coefficient (r2) ranged from 0.9971 to 0.9983. The limits of detection and limits of quantification ranged from 0.5 to 1.0 µg/kg and 1.5 to 3.0 µg/kg, respectively. Accuracy and precision were determined by spiking salmon and chicken samples with 3.0, 10.0, and 100.0 µg/kg of analytes, in compliance with the current legislation, with six replicates per determination. The average recoveries of the seven QACs ranged from 65.4% to 101%. The relative standard deviations (RSDs) were between 0.64% and 16.8%. Matrix effects of the analytes were between -27.5% and 33.4% in salmon and chicken samples after purifying using PSA. The developed method was applied to the determination of seven QACs in rural samples. QACs were detected in only one sample; the level did not exceed European Food Safety Authority specified residue limit standards. The detection method has high sensitivity, good selectivity and stability, and the results are accurate and reliable. It is suitable for the simultaneous rapid determination of seven QAC residues in frozen food. The results provide valuable information for future risk assessment studies targeting this class of compounds.

Systematic research of H2dedpa derivatives as potent inhibitors of New Delhi Metallo-ß-lactamase-1.

New Delhi Metallo-ß-lactamase-1 (NDM-1), a Zn (II)-dependent enzyme, can catalyze the hydrolysis of almost all ß-lactam antibiotics including carbapenems, resulting in bacterial antibiotic resistance, which threatens public health globally. Based on our finding that H2dedpa is as an efficient NDM-1 inhibitor, a series of H2dedpa derivatives was systematically prepared. These compounds exhibited significant activity against NDM-1, with IC50 values 0.06-0.94 µM. In vitro, compounds 6k and 6n could restore the activity of meropenem against Klebsiella pneumoniae, Escherichia coli and Proteus mirabilis possessing either NDM or IMP. In particular, the activity of meropenem against E. coli producing NDM-4 could be improved up to 5333 times when these two compounds were used. Time-kill cell-based assays showed that 99.9% of P. mirabilis were killed when treated with meropenem in combination with compound 6k or 6n. Furthermore, compounds 6k and 6n were nonhemolytic (HC50 > 1280 µg/mL) and showed low toxicity toward mammalian (HeLa) cells. Mechanistic studies indicated that compounds 6k and 6n inhibit NDM-1 by chelating the Zn2+ ion of the enzyme.