Quantitative analysis of fluorinated ethylchloroformate derivatives of protein amino acids and hydrolysis products of small peptides using chemical ionization gas chromatography mass spectrometry

The derivatization and extraction efficiencies of 16 protein amino acids were investigated using trifluoroethanol + ethylchloroformate + pyridine as the derivatization reagents and chloroform as the solvent. The derivatization efficiencies ranged from 90% to 99% for all the amino acids studied except aspartic acid (79%). The extraction efficiencies of the derivatized amino acids using chloroform were close to 100%. In addition, the detection limits and linear dynamic ranges of trifluoroethanol ethylchloroformate (TFE-ECF) derivatives of these amino acids were studied using positive-ion chemical ionization gas chromatography-mass spectrometry (GC-MS). The detection limits of the protein amino acids were mostly in the low femtomole range. The linear dynamic ranges of these amino acids were in the range of zero to three orders of magnitude. The GC-MS analysis of the derivatized amino acids was applied to the hydrolysis products of Equal, a sugar substitute containing aspartame and diprotin B, a tripeptide. The results demonstrate that the TFE-ECF derivatization of the hydrolysis products of small peptides followed by GC-MS analysis can be used for the identification of their amino acid composition (except arginine) and for their complete amino acid analysis.