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.
Keywords: Chromatography; Food quality control; Matrix effect; Measurement uncertainty; Medical nutrition therapy; Taurine (PubChem CID: 1123); l-alanine (PubChem CID: 5950); l-arginine (PubChem CID: 6322); l-aspartic acid (PubChem CID: 5960); l-glutamic acid (PubChem CID: 33032); l-histidine (PubChem CID: 6274); l-isoleucine (PubChem CID: 6306); l-phenylalanine (PubChem CID: 6140); l-tryptophan (PubChem CID: 6305); l-tyrosine (PubChem CID: 6057).
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