m/z = 111+R fragment in the mass spectra of HMT-R-H derivatives suggests a fragmentation mechanism involving the loss of one of the CH₂N groups (highlighted in blue) upon ionisation in the filament of the QMS adjacent to the CH-R-H group (where R-H represents the characteristic side group of each HMT derivative, e.g. CH₃, NH₂, OH, and CHO), giving rise to fragments with a mass of 111 + R g/mol.