称取乳粉样品1.000 g，加入1.0 mol·L^-1的盐酸溶液25 mL，涡旋混匀5 min，于70℃水浴中水解3 h （每隔30 min振摇混匀一次），冷却后加入20 mL乙醚，涡旋振荡30 s，然后于4℃下以6 000 r·min^-1冷冻离心10 min。取上清液0.10 mL，加入1 mol·L^-1的乙酸铵溶液50 μL，用水定容至10.0 mL，涡旋混匀，吸取1~2 mL上清液，经0.22 μm水系针式滤膜过滤后，采用Hypersil GOLD^TM AQ色谱柱（2.1 mm×100 mm，1.9 μm）分离，以乙腈-乙酸铵溶液为流动相进行梯度洗脱。质谱选择电喷雾正离子源和多反应监测模式。胆碱和左旋肉碱的质量浓度分别在0.05~1.0 mg·L^-1，0.01~0.20 mg·L^-1内与其定量离子峰面积呈线性关系，检出限（3S/N）分别为0.003，0.005 mg·kg^-1。方法用于测定质控样品中的胆碱和左旋肉碱，测定值与认定值的相对误差在10%以内。采用本方法测定婴幼儿配方乳粉样品中的胆碱和左旋肉碱，测定结果和国家标准方法的测定结果相符，测定值的相对标准偏差（n=6）小于9.0%

The milk powder sample (1.000 g) was taken and 25 mL of 1.0 mol·L^-1 hydrochloric acid solution was added. After vortex mixing for 5 min, the mixture was hydrolyzed in 70℃ water bath for 3 h (shaking and mixing once every 30 min) and cooled. Then 20 mL of ether was added and the mixture was vortexed for 30 s, centrifuged at 6 000 r·min^-1 for 10 min at 4℃. 0.10 mL of the supernatant was taken and 50 μL of 1 mol·L^-1 ammonium acetate solution was added. The mixture was diluted to 10.0 mL with water. After vortex mixing, 1-2 mL of the supernatant was passed through a 0.22 μm water-based needle filter. The filtrate was separated on a Hypersil GOLD^TM AQ column (2.1 mm×100 mm, 1.9 μm), with a mixture of acetonitrile and ammonium acetate solution as mobile phase in gradient elution. Electrospray positive ion source and multiple reaction monitoring mode were selected in mass spectrometry analysis. Linear relationships were found between the peak area of quantitative ions and the mass concentration of choline and L-carnitine in the range of 0.05-1.0 mg·L^-1 and 0.01-0.20 mg·L^-1, respectively. The detection limits (3S/N) were 0.003, 0.005 mg·kg^-1, respectively. The proposed method was used to determine choline and L-carnitine in the quality control sample, giving the relative error between the measured values and the certified values within 10%. Choline and L-carnitine in infant formula milk powder samples were determined by the proposed method, the results were consistent with those obtained by the national standard method, and RSDs (n=6) were less than 9.0%.