样品0.500 g于50 ℃用甲醇10 mL超声萃取30 min。取萃取液4 mL，加入5 mmol·L^-1乙酸铵溶液6 mL，摇匀、过滤。采用超高效液相色谱-串联质谱法对所得溶液中的全氟十一烷酸、全氟十二烷酸、全氟十三烷酸和全氟十四烷酸等4种长链全氟烷酸进行测定。以ACQUITY UPLC BEH C₁₈色谱柱为固定相，以不同体积比的5 mmol·L^-1乙酸铵溶液和甲醇的混合液为流动相进行梯度洗脱。质谱分析中采用电喷雾负离子源和多反应监测模式，锥孔电压分别为50，20，28，24 V。结果表明，4种长链全氟烷酸的质量浓度在1.00~100 μg·L^-1内与峰面积呈线性关系，检出限（3S/N）为0.4~0.6 μg·L^-1。按标准加入法进行回收试验，回收率为86.8%~96.4%，相对标准偏差（n=7）为3.7%~9.7%。

The sample of 0.500 g was extracted ultrasonically with methanol of 10 mL for 30 min at 50℃. The extract of 4 mL was taken and 5 mmol·L^-1 ammonium acetate solution of 6 mL was added. The solutions were mixed and filtered. Four long-chain perfluoroalkyl acids (PFuDA, PFDoA, PFTriDA and PFTeDA) in the above solution were determined by UPLC-MS/MS, and ACQUITY UPLC BEH C₁₈ column was used as the stationary phase and the mixture of 5 mmol·L^-1 ammonium acetate solution and methanol in different volume ratios was used as the mobile phase for gradient elution. Negative electrospray ion source and multi reaction monitoring mode were adopted in MS analysis, and cone voltages were 50, 20, 28, 24 V, respectively. As shown by the results, Linear relationships between values of peak area and mass concentration of 4 long-chain perfluoroalkyl acids were found in the range of 1.00-100 μg·L^-1, with detection limits (3S/N) in the range of 0.4-0.6 μg·L^-1. Test for recovery was made by standard addition method, giving results in the range of 86.8%-96.4%, with RSDs (n=7) ranged from 3.7% to 9.7%.