Rapid Quantitative Analysis of Amino Acids in Compound Amino Acid Injection Using Presaturation Water Suppression NMR Spectroscopy

Compound amino acid injection (CAAI) is an injectable preparation containing multiple amino acids, clinically indicated for patients with impaired protein intake, absorption disorders, or unmet nutritional needs. Conventional chromatography-based methods for detecting the amino acids require derivatization and are time-consuming. In this study, a quantitative nuclear magnetic resonance (qNMR) technology combined with water suppression by presaturation was developed for rapid quantification of nine amino acids in CAAI-9AA, in which 9AA serves as a specification code denoting a formulation comprising nine amino acids. Maleic acid (MA) and 3-(trimethylsilyl)propionic acid-d4 sodium salt (TMSP) were employed as dual internal standards, and deuterated pyridine as a chemical shift reagent and pH adjuster. Method validation demonstrated excellent agreement with reference liquid chromatography results (deviation within ± 3%). The assay showed good linearity (R 2 ≥ 0.999) within a certain concentration range and exhibited excellent precision and repeatability with a relative standard deviation (RSD) below 2.0%. The recovery values were between 96.75 and 108.10%. This validated qNMR method enables rapid and accurate quantification of amino acid components, confirming its practicality for routine pharmaceutical analysis and providing a novel, feasible strategy for the quantitation of more component amino acid formulations.