The water loss process in Laser Mass Spectrometry of amine terminal amino acids was studied. Water loss is proposed to occur via a thermal decomposition mechanism for a protonated amino acid forming a protonated lactam ring. The magnitude of the water loss peak is correlated with the stability of the protonated lactam ring. Semi-empirical MNDO calculations of the heat of reaction of a protonated amino acid forming a protonated lactam ring and water support the correlation. The substrate (matrix) appears to have little effect on the process; results are essentially the same with the use of different substrates and sample preparation methods.
Kenneth J. Rosnack, Kasi V. Somayajula, Andrew G. Sharkey, Nancy J. Jensen, and David M. Hercules, "Determination of Water Loss Mechanism in Amine Terminous Amino Acids Using Laser Mass Spectrometry," Appl. Spectrosc. 43, 1087-1092 (1989)