The origin and ion spectra of non-covalent peptide dimers observed in liquid secondary ion mass spectrometry explained via first-order gas-phase kinetics

Static liquid secondary ion mass spectra were generated for a variety of dipeptides dissolved in common liquid secondary ion mass spectrometric matrices. The relationship of the ion intensities of the monomer and non-covalent dimers was examined in order to determine the origin of non-covalent dimerization. The results demonstrate that the ion intensities are independent of solution equilibria and are indicative of first-order gas-phase kinetics.