Abstract:

Nitroimidazoles (NMZs) are a crucial group of antibacterial compounds from a historical perspective. In the past, they were used for treating and preventing parasitic infections in fish. Benzodiazepines (BZDs) are second-generation sedative-hypnotics. Some fish farmers or vendors use them illegally to keep aquatic products fresh during the transportation of aquatic animals. Aquatic products are one of the most common food sources of protein and can be contaminated by NMZs and BZDs, which could impact humans through the food chain. Until recently, there was limited information on the simultaneous determination of NMZs and BZDs. Thus, it is critical to accurately quantify NMZs and BZDs for risk assessment and risk monitoring of food safety.
For the simultaneous determination of five nitroimidazoles and six benzodiazepines in aquatic products, a new approach based on the dispersive solid-phase extraction (dSPE) coupled with ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) was developed. First, the samples were extracted with acetonitrile containing 1% (v/v) ammonium hydroxide, and the extracts were purified using dSPE with C18 and primary secondary amine sorbents. Second, the extracts were collected and dried at 45 ℃ under nitrogen flow. Finally, the extracts were redissolved in 1 mL methanol-water (1∶9, v/v) mixture, filtered through a nylon-66 microfiltration membrane, and analyzed using UHPLC-MS/MS. The separation of compounds was conducted on a Kinetex F5 column (100 mm×3.0 mm, 2.6 μm) using gradient elution with 1% (v/v) formic acid aqueous solution and methanol as the mobile phase. The analytes were detected using MS/MS with positive electrospray ionization (ESI⁺) source under the multiple reaction monitoring modes. The matrix-matched external standard approach was used for quantitative analysis. The compounds of five nitroimidazoles and six benzodiazepines could be examined within 8.5 min. Under the optimal conditions, the standard curves were linear in the range of 0.5-20 μg/L, with the correlation coefficients exceeding 0.995. The limits of detection and limits of quantification were 0.2-0.5 μg/kg and 0.5-1.0 μg/kg, respectively. The average recoveries at three spiked levels in blank samples (grass carp, large yellow croaker, and prawn) ranged from 73.2% to 110.6%, with relative standard deviations of less than 15%. The developed approach is simple, sensitive, fast, and inexpensive. It can be used for determining five nitroimidazoles and six benzodiazepines in aquatic products.

Key words: ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS), dispersive solid-phase extraction (dSPE), nitromidazoles, benzodiazepines, aquatic products