A high-performance liquid chromatography (HPLC) method was developed and validated for the simultaneous determination of 18 amino acids in special formula milk powder. This method was based on pre-column derivatization with phenyl isothiocyanate, separation on a C₁₈ column, ultraviolet detection, and quantification using external standards. Acid hydrolysis using 6 mol/L HCl under autoclaving at 120 °C for 2 h was optimized and compared with conventional oven hydrolysis at 110 °C for 24 h. The results revealed that all 18 amino acids yielded linear correlation coefficients exceeding 0.999. The limits of detection and quantification ranged from 0.07 to 0.32 μg/mL and from 0.23 to 1.07 μg/mL, respectively. The precision, repeatability, and stability were 0.06%–2.44%, 0.32%–2.22%, and 0.19%–2.77%, respectively, and the spiked recoveries ranged between 85.92% and 107.55%. The developed method allowed the analytical run time for all amino acids to be reduced to 35 min. Another advantage was that the proposed method enabled quantification of tryptophan, asparagine, and glutamine, which are not detected by the standard method defined in GB 5009.124–2016 National food safety standards–determination of amino acids in food. Overall, the obtained results demonstrate that our method allowed the simultaneous quantification of 18 amino acids in special formula milk powder with improved precision, sensitivity, and efficiency after optimization of the hydrolysis and detection conditions. This method is expected to prove suitable for the quality control of foods for special medical purposes.

In the future, the supply and variety of foods for special medical purposes (FSMPs) available on the market are expected to keep increasing. However, no fatty acid detection method specifically for FSMPs, especially special formula milk powder, has yet been established in China. This paper reports a rapid and accurate method based on gas chromatography-mass spectrometry (GC-MS) for the determination of fatty acids in special formula milk powder. The results showed that ultrasound-assisted lipid extraction in the solution state, methyl esterification of the fatty acids with the solution of sodium methoxide in methanol, a defined GC-MS temperature program, and a split ratio of 10:1 gave the best results. The linearity (correlation coefficients: 0.995 9–0.999 7), precision (relative standard deviation (RSD): 0.41%–3.36%), stability (RSD: 1.01%–4.91%), repeatability (RSD: 1.02%–3.81%), and spiked recovery rate (90.03%–107.76%) of the proposed method were confirmed to meet the detection requirements. Finally, the method performance was evaluated for nine commercial products, and the results revealed that the method was cheaper than that used in the national standard for the determination of fatty acids in food (GB 5009.168–2016) and the analysis time was shortened by 0.5 h. Compared to the international standard for the determination of fatty acids (AOAC 996.06), this method subdivides fatty acids and is more comprehensive in terms of detection accuracy and applicability. In conclusion, the proposed method enables the efficient and accurate detection of fatty acids in FSMPs.