[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.

[Simultaneous determination of beauvericin and four enniatins in eggs by ultra-performance liquid chromatography-tandem mass spectrometry coupled with cold-induced liquid-liquid extraction and dispersive solid phase extraction].

Enniatins (ENNs) and beauvericin (BEA), known as emerging mycotoxins, are the toxic secondary metabolites produced by various Fusarium species. Most grain and grain-based products are contaminated with ENNs and BEA. Animals have been exposed to ENNs and BEA primarily due to consumption of cereal grains and cereal by-products. ENNs and BEA have been detected in animal-derived food and human breast milk, and they pose significant threats to public health. Therefore, more contamination data are urgently needed for the risk assessment of ENNs and BEA present in animal-derived food. To ensure the quality of animal-derived food, a method has been developed for the simultaneous detection of five emerging mycotoxins (viz. enniatin B, enniatin B1, enniatin A, enniatin A1, and beauvericin) in eggs by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) coupled with cold-induced liquid-liquid extraction (CI-LLE) and dispersive solid phase extraction (DSPE). The main factors governing the response, recovery, and sensitivity of the method, such as the type of extraction solvent, the temperature and duration of cold treatment in CI-LLE, the type and dosages of adsorbents, and apparatus conditions and the type of mobile phase used, were optimized during sample pretreatment and instrument analysis. The mycotoxin residues in eggs were extracted using 20 mL acetonitrile-water-acetic acid (79∶20∶1, v/v/v) mixture for 20 min by the vortex shock method. After mixing, the mixture was frozen for 30 min in a freezer at -40 ℃ and centrifuged for 10 min at 10000 r/min. A 2 mL aliquot of the upper acetonitrile layer was purified by using 70 mg of C18 adsorbents. After whirling, the mixtures were centrifuged at 10000 r/min for 5 min. The purified solution was then concentrated to nearly dry in nitrogen atmosphere at 40 ℃. The residues were dissolved in 1.0 mL 80%(v/v) acetonitrile aqueous solution. The target analytes were separated on an ACQUITY UPLC BEH C18 chromatographic column (100 mm×2.1 mm, 1.7 µm) at a column temperature of 40 ℃, with a flow rate of 0.3 mL/min. The injection volume was 5 µL, and gradient elution was conducted using acetonitrile and 5 mmol/L ammonium formate solution as the mobile phases. Multiple reactions monitoring (MRM) was conducted in the positive electrospray ionization (ESI +) mode. The isotope internal standard method was used for quantification of BEA, and the matrix-matched external standard method was used for quantification of four ENNs. The results of the optimized method showed that the five analytes were completely separated by using the above-mentioned chromatographic column. Good linear relationships were obtained for the five mycotoxins in the concentration range of 0.1-50.0 µg/L; the correlation coefficient (r2) ranged from 0.9983 to 0.9997. The limits of detection (LODs) ranged from 0.05 to 0.15 µg/kg, while the limits of quantification (LOQs) ranged from 0.20 to 0.50 µg/kg. Accuracy and precision experiments were conducted by spiking egg samples with known amounts of analytes at three concentration levels (0.5, 5.0, and 25.0 µg/kg, in compliance with the current legislation) with six replicates. The average recoveries of the five analytes ranged from 81.1% to 106%, and the relative standard deviations (RSDs) were between 0.27% and 9.79%. The matrix effects of the analytes were between 2.70% and 45.1% in egg samples after pretreatment by CI-LLE coupled with DSPE. The developed method was applied to the determination of five mycotoxins in rural eggs and commercial eggs. BEA was detected in most rural egg samples, with detection rates of 30.4%. None of the four ENN residues were detected. Therefore, we can conclude that the method described herein has the advantages of sensitivity, stabilization, accuracy, good recovery, and easy operation, and is suitable for the simultaneous and rapid determination of BEA and ENN residues in eggs.

A novel highly fluorescent S, N, O co-doped carbon dots for biosensing and bioimaging of copper ions in live cells.

In this study, novel highly fluorescent sulfur, nitrogen, and oxygen co-doped carbon dots (S, N, O-CDs) were prepared from m-phenylenediamine and sulfamide by using the hydrothermal method. The prepared S, N, O-CDs show high doping rate and fluorescence yield as well as long-term fluorescence stability. In addition, S, N, O-CDs show good fluorescence response towards Cu2+ over a concentration range of 2-60 µM with a detection limit of 0.29 µM. Taking advantages of the properties of S, N, O-CDs including high selectivity and low cytotoxicity, S, N, O-CDs were successfully applied for Cu2+ sensing and imaging in the cells and O2˙--induced Cu2+ increase in the cells was observed. Furthermore, on account of strong complexation between Cu2+ and pyrophosphate ion (PPi) as well as specific hydrolysis ability of alkaline phosphatase (ALP) towards PPi, PPi and ALP were further detected with high selectivity based on S, N, O-CDs/Cu2+ system. The prepared S, N, O-CDs showed good detection results for PPi and ALP with detection limits of 0.44 µM and 1.03 U L-1, respectively. Moreover, the developed method also realized PPi and ALP detection in real samples.