Accurate and efficient amino acid analysis for protein quantification using hydrophilic interaction chromatography coupled tandem mass spectrometry

Table 3 Calculated amounts of labile amino acids, after different hydrolyses, represented in percentage of total protein, BSA

Analyte	Expected (%)	Observed (%, LC–MS/MS)			Observed (%, AccQ-Tag)
Analyte	Expected (%)	H₂O₂ + 6 M HCl + β-ME	6 M HCl + β-ME	4 M MetS + 0.2% tryptamine	H₂O₂ + 6 M HCl + β-ME	6 M HCl + β-ME	4 M MetS + 0.2% tryptamine
Cys*	5.77	5.3 ± 0.51	4.23 ± 0.32	4.56 ± 0.34	5.38 ± 0.10	1.11 ± 0.06	1.75 ± 0.32
Met*	0.82	ND	0.79 ± 0.01	0.76 ± 0.01	1.52 ± 0.02	0.29 ± 0.01	0.46 ± 0.02
Trp	0.49	ND	ND	0.59 ± 0.02	0.04 ± 0.00	0.05 ± 0.00	0.23 ± 0.01

Variability is expressed as standard error of mean (n = 3). ND, not detected
*Cysteine was measured as cysteic acid in hydrolysis that involved prior oxidation and as cystine otherwise. Similarly, methionine was measured as methionine sulfoxide upon oxidation and as methionine in the two methods that did not involve prior oxidation

ISSN: 1746-4811