Determination of 19 Free Amino Acids and Taurine in Formulas for Special Medical Purpose Intended for Infants by Ultra-high Performance Liquid Chromatography

An ultra-high performance liquid chromatography (UPLC) method was developed for the simultaneous determination of 19 free amino acids and taurine in formulas for special medical purpose intended for infants. The samples were hydrolyzed by α-amylase, and purified by precipitating proteins and other impurities through pH adjustment. The method was based on pre-column derivatization with 6-aminoquinolinyl-N-hydroxysuccinimidate (AQC). Formic acid-ammonium formate (20 mmol/L, pH 2.25), formic acid-ammonium formate (20 mmol/L, pH 3.00), and acetonitrile were used as mobile phases A, B and C for gradient elution, respectively. The analytes were separated on an AccQ-Tag Ultra C₁₈ column, detected with a diode-array detector and quantified by an external standard method. Good linearity was observed for cystine in the range of 5–125 μmol/L and 18 other amino acids and taurine in the range of 10–250 μmol/L with correlation coefficients higher than 0.999. The limit of detection (LOD) was 1.5 μmol/L for cystine, and 3 μmol/L for the other analytes. The limit of quantitation (LOQ) was 5 μmol/L for cystine, and 10 μmol/L for the other analytes. The average recoveries of the method were in the range of 90.16%–109.84% with relative standard deviation (RSD) not more than 4.77%. The method was easy to operate, accurate and highly reproducible, and could be suitable for the determination of 19 amino acids and taurine in formulas for special medical purpose intended for infants, providing strong technical support for enterprise quality control and government regulation.