Simultaneous Determination of 15 Cephalosporins in Aquatic Products by Ultra-High Performance Liquid Chromatography-Tandem Mass Spectrometry with Isotope Dilution

A method for the simultaneous determination of 15 cephalosporins in aquatic products by ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) was proposed. 200 μL of 100 μg·L^-1 isotope internal standard mixed solution was added into 5 g of the processed sample with settling for 30 min. Then 2 g of acidic alumina was added, and the sample solution was extracted twice with 5 mL of 80% (φ) acetonitrile solution. The supernatant combined was transferred to Oasis Prime HLB solid phase extraction small column. The collected eluate was blown to about 1 mL with nitrogen at 40 ℃. Then 1 mL of acetonitrile solution containing 0.1% (φ) formic acid was added, and 0.22 μm nylon membrane was used to filter. Agilent InfinityLab Poroshell 120 SB C₁₈ column was used as the stationary phase, and a mixture of 0.1% (φ) formic acid solution and acetonitrile at different volume ratios was used as the mobile phase for gradient elution. ESI⁺ and MRM mode were selected, and internal standard method was used for quantitative analysis. As shown by the results, linear relationships between values of mass concentration of 15 cephalosporins and ratios of its response value to internal standard response value were kept in definite ranges, with detection limits (3S/N) in the range of 0.3-2.0 μg·kg^-1. Recovery test was made on blank samples at 3 concentration levels by standard addition method, giving results in the range of 75.9%-119%, and RSDs (n=6) of the determined values were in the range of 1.6%-6.5%. This method has been applied to the analysis of actual samples, and cephalexin was detected in one grass carp sample with detection amount of 3.78 μg·kg^-1.