Amino acid composition analysis (AAA) determines the molar ratio of each amino acid residue in a peptide or protein sample following complete hydrolysis of peptide bonds. It is a foundational analytical technique used for identity confirmation, content determination, and quality control of protein therapeutics and peptide APIs.
The standard workflow begins with acid hydrolysis — typically 6M HCl at 110°C for 20–24 hours under vacuum or inert atmosphere. This cleaves all peptide bonds but simultaneously destroys tryptophan (requires alkaline hydrolysis or special conditions) and partially destroys serine, threonine, and methionine.
Following hydrolysis, free amino acids are derivatized (pre-column or post-column) to enable UV or fluorescence detection. Common reagents include phenylisothiocyanate (PITC, Waters PicoTag method), ortho-phthalaldehyde (OPA), and 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AccQ•Tag, UPLC compatible).
UPLC-based AccQ•Tag methodology has largely replaced traditional HPLC approaches for AAA, offering significantly reduced analysis times (under 10 minutes per sample), higher sensitivity, and improved resolution of co-eluting residues. SynthAxis uses UPLC-AAA as the default method for routine composition confirmation.
Common analytical challenges include incomplete hydrolysis of hydrophobic sequences (especially Val-Val, Ile-Ile dipeptides), destruction of labile residues, and accurate quantitation of low-abundance residues in complex protein matrices. Each requires specific method adaptations.
For regulatory submissions (USP, EP, JP compliance), AAA is performed according to validated methods with appropriate reference standards, calibration curves, and system suitability parameters. SynthAxis can provide full validation documentation for AAA methods used in GMP release testing of peptide APIs.