Validation of an Ion-Interaction Chromatography Analysis of Underivatized Amino Acids in Commercial Preparation Using Evaporative Light Scattering Detection

A liquid chromatographic procedure using ion interaction reagent and evaporative light scattering detection was developed and validated for the direct quantification of 8 underivatized amino acids (threonine, lysine, valine, methionine, isoleucine, leucine, phenylalanine and tryptophan) present simultaneously in a commercial preparation. The chromatographic separation was achieved on a Purospher RP-18e column with an acetonitrile gradient and using heptafluorobutyric acid as volatile ion interaction reagent. Acceptable levels of linearity, specificity, precision, accuracy, robustness and limits of detection were achieved during the validation of the method. Detection limits varied from 1 mg.L−1 to 2 mg.L−1 depending on the amino acid being analyzed. The results of this method agree to within 98.6%–102.5% when compared to the manufacturer’s certificate of analysis obtained with the standard amino acid autoanalyser method. This approach yields a simple, universal method that is well suited for amino acid analysis, when a sufficient quantity is available. Only basic LC instrumentation with an ELSD is necessary for this procedure.