A comparison of internal and external standardization in amino acid analysis.

To assess quantitatively the merits of internal standardization, an amino acid mixture of known composition has been analyzed by conventional automated amino acid analysis before and after being subjected to total acid hydrolysis. Both the precision (reproducibility) and the accuracy (lack of bias) were generally, but not invariably, greatly enhanced by the use of internal standardization with norleucine as opposed to external standardization. Incorporation of internal standards into samples is strongly recommended.