This study investigates the fragmentation of organic molecules under mass spectrometric conditions with a special focus on the identification of oxidized amino acids in peptide chains. The initial experimental setup involved the use of a mass spectrometer equipped with sodium trifluoroacetate (NaTFA) dissolved in methanol as a solvent. The study examined in detail the fragmentation behavior of the GTHSMKHM peptide with a focus on the oxidation of specific amino acid residues. Oxidized forms were identified by molecular weight analysis using specialized software, confirming the presence of oxidized histidine and its impact on the peptide structure. This research identified that oxidation occurred specifically on the histidine residue. This conclusion was drawn by comparing the MS spectra of the oxidized and non-oxidized oligopeptides.