Magnetic one-step purification-high performance liquid chromatography-triple quadrupole/composite linear ion trap mass spectrometry for the determination of 54 veterinary drug residues in carp

Aquatic food products contain interfering substances， such as fats and proteins， which affect the analysis and detection of target compounds by significantly reducing detection efficiency and contaminating detection instruments. Effectively removing interfering substances is a key step in the field of food quality testing. To reduce the influence of interfering substances in aquatic products， this study established a detection method for 54 veterinary drug residues in carp by using magnetic one-step purification combined with high performance liquid chromatography-triple quadrupole/composite linear ion trap mass spectrometry （HPLC-QTRAP-MS/MS）. The purification process uses solvothermally synthesized spherical magnetite as the magnetic material. This material is strongly magnetic and enables impurities to be efficiently separated and collected. Additionally， a metal-organic framework material with an amino-rich surface （ZIF-67） was self-assembled to serve as the purifying agent. ZIF-67 is particularly effective at removing polar impurities during the magnetic one-step purification process. Scanning electron microscopy confirmed the successful synthesis of both materials， ensuring their structural integrity and suitability for the intended application.Acetonitrile was chosen as the extraction solvent owing to its excellent solubilizing properties. Furthermore， formic acid was added to enhance the extraction efficiencies of acidic veterinary drugs. Anhydrous sodium sulfate was used to remove water from the matrix， thereby further improving the purity of the extract. The extract underwent magnetic one-step purification following centrifugation， which effectively removed interfering substances while preserving the target compounds. Chromatographic separation was achieved using the C₁₈ RRHD column （15 cm×4.6 mm， 2.7 µm）， with 5 mmol/L ammonium acetate solution （containing 0.2% formic acid） and 0.2% formic acid in methanol used as mobile phases. HPLC-QTRAP-MS/MS was then used to separate and determine the analytes， with data collected in multiple reaction monitoring （MRM） mode. The 54 veterinary drugs were quantitatively analyzed using matrix-matched standard curves， thereby ensuring accurate quantification even for complex matrices. Various parameters that affect the purification fillers were investigated to optimize the purification process. Octadecyl-bonded silica gel （C₁₈） was used as an auxiliary purification material as it is known to effectively remove non-polar impurities. Combining 60 mg of ZIF-67 with 50 mg of C₁₈ yielded the best purification results. All 54 compounds exhibited weak matrix effects after pretreatment and purification， with a value of only 18.11% recorded for the compound that exhibited the most significant matrix effect. The 54 veterinary drugs exhibited excellent linear relationships between response and concentration in the 0.5-50.0 µg/L range， with all coefficients of determination （r²） above 0.99. Detection and quantification limits of 0.5-1.0 and 1.0-2.0 µg/kg were recorded， respectively. The performance of the method was evaluated by spiking blank carp matrix samples at three concentrations （2.0， 5.0， and 20.0 µg/kg）. The recovery rates of the spiked samples ranged between 81.34% and 109.85%， and intra-day and inter-day relative standard deviations were less than 10%. The rapidity and accuracy of the developed method were assessed through comparisons with existing veterinary-drug detection methods， which revealed that the developed method is more sensitive and repeatable. Furthermore， the feasibility of the established detection method was verified by testing commercial aquatic products. No target veterinary drugs were detected in actual samples， which highlights the reliability of the developed method. In conclusion， the method developed in this study provides an effective means of monitoring veterinary drugs in carp. It meets the requirements of economy， simplicity， and efficiency while exhibiting high sensitivity and reproducibility. The developed approach represents a significant advancement in the field of aquatic food safety testing and is expected to ensure more accurate and reliable detection of veterinary drug residues.