Process of mass spectroscopic analysis of peptide ladders generated in gas phase ammonia. A peptide (with amino acids AA1 through AA5 in the scheme) is synthesized on a solid support (represented as a gray circle). The N-terminal amine is labeled by a group with a permanent positive charge. This is subjected to high pressure ammonia gas which randomly cleaves peptide bonds, resulting in a series of N-terminal labeled fragments. Generally, only the charge-labeled fragments give a strong signal in the mass spectrum. Upon MALDI mass spectrometry, one sees a series of peaks that correspond to masses separated by single amino acid molecular weights.