经均浆处理的羊内脏器官样品采用0.2 mol·L^-1乙酸铵缓冲溶液提取，酶解反应6 h后，冷却至室温，加入10 μg·L^-1莱克多巴胺-D3内标溶液。加入0.1 mol·L^-1高氯酸溶液除去提取液中的蛋白质后，用乙酸乙酯萃取2次，合并乙酸乙酯层，浓缩至干，加入20%（体积分数）甲醇溶液溶解残渣，再加入经乙腈饱和的正己烷。移取下层过0.22 μm滤膜，采用高效液相色谱-串联质谱法测定滤液中莱克多巴胺的含量。以Hypersil GOLD C₁₈色谱柱为固定相，以不同体积比的0.1%（体积分数）甲酸溶液和甲醇的混合液为流动相进行梯度洗脱，串联质谱分析中采用电喷雾离子源正离子扫描模式和多反应监测模式。采用同位素内标法定量，甲醇的质量浓度在0.25~5.0 μg·L^-1内与其对应的峰面积呈线性关系，检出限（3S/N）为0.3 μg·kg^-1。以空白样品为基体进行加标回收试验，所得回收率为81.4%~90.2%，测定值的相对标准偏差（n=6）为0.89%~1.4%。

The homogenized sample of internal organ of sheep was extracted with 0.2 mol·L^-1 ammonium acetate buffer solution. After enzymatic hydrolysis for 6 h, the sample solution was cooled to room temperature and then 10 μg·L^-1 internal standard solution of ractopamine-D3 was added. The extract was removed protein with 0.1 mol·L^-1 perchloric acid solution and then extracted 2 times with ethyl acetate. The ethyl acetate layers were combined and concentrated to dryness. The residue was dissolved with 20% (φ) methanol solution and n-hexane saturated with acetonitrile was added. The lower level was taken and then filtered on 0.22 μm filtering membrane. HPLC-MS/MS was applied to the determination of ractopamine in the filtrate. Hypersil GOLD C₁₈ chromatographic column was used as stationary phase, and the mixture of 0.1% (φ) formic acid solution and methanol mixed in different ratios was used as mobile phase in gradient elution. ESI⁺ and multi-reactions monitor mode were adopted in MS/MS. Isotope was used as internal standard. Linear relationship between values of peak area and mass concentration of methanol was kept in the range of 0.25-5.0 μg·L^-1, with detection limit (3S/N) of 0.3 μg·kg^-1. On the base of blank sample, test for recovery was made by standard addition method; values of recovery found were in the range of 81.4%-90.2%, with RSDs (n= 6) of determined values in the range of 0.89%-1.4%.