Development, validation, and uncertainty measurement of HPLC-DAD method for determination of some free amino acids in infant formula and medical food products for inborn errors of metabolism

This research aims at determining some free amino acids in amino acid-based infant formulas and amino acid-modified medical foods for inborn errors of metabolism to prove their quality. A method based on high-performance liquid chromatography and diode array detection was developed and validated. Then, overall uncertainty was estimated by the bottom-up approach. Applying the weighted least squares regression method suggested good linearity with coefficient of determinations ≥ 0.9960. The limits of detection were calculated between 0.01 and 0.28 μg/mL. The most repetitive recovery values were obtained in the range of 91–108%, with RSDs ≤ 15%. The expanded uncertainties were below 20% for most amino acids. The contributions of linear regression and repeatability are two main factors in estimating overall uncertainty. The results offer this method as a simple and easy procedure for analyzing free amino acids in seven powdered medical foods designed for phenylketonuria, maple syrup urine disease, methylmalonic, and propionic acidemia.