A Rapid and Sensitive Method for Free Amino Acids in Nasal Feeding Nutrition by Liquid Chromatography with Liquid Extraction-Derivatization

A rapid and sensitive liquid chromatography method was developed and validated for the simultaneous determination of 21 free amino acids in nasal feeding nutrition after liquid extraction-derivatization. The analytes were extracted by PEG/EtOH (60/40, v/v), concentrated by a Dowex Monosphere 650C cation-exchange resin and derivatized using phenyl isothiocyanate (PITC). The separation was carried out on a reversed-phase Shimadzu Inertsil ODS-3 column with component A 10 mmol L−1 phosphate buffer solution (pH 6.5) and B acetonitrile/methanol/water (40/45/15, v/v/v). The optimal separation of 21 amino acids was obtained within 15 min. The average recoveries of 21 amino acids spiked at 3 concentrations (0.5, 2.0 and 10.0 µmol L−1) were in the range of 62.49–82.54%. Limits of detections (LODs) varied from 0.002 to 0.038 µmol L−1 and limits of quantifications (LOQs) ranged from 0.01 to 0.19 µmol L−1. This rapid and sensitive method has been successfully applied for the analysis of nasal feeding nutrition from Chinese markets, and the contents of free amino acids in these samples are very different.