Mass spectrometry of biopolymers based on ion-induced desorption

Abstract: Various aspects of biopolymer molecular characterization by their molecular masses havebeen studied, with emphasis on ion-induced desorption and time-of-flight mass Spectrometry(TOF MS). Limitations of the average-isotopic mass concept, as well as the utility ofaccurate monoisotopic mass measurements for deriving amino-acid and elementalcompositions, are discussed. A new sufficiency criterion of mass accuracy for peptidecharacterization is formulated. Experimentally achievable mass accuracy in TOF MS basedon MeV-ion induced desorption is studied. A new method of deriving peptide structuralinformation using partial acid hydrolysis and accurately measured hydrolysis fragmentmasses is developed.Secondary ion formation mechanisms in ion-induced desorption have been studiedusing keV and MeV atomic and polyatomic projectiles. In the MeV-atomic-ion mode, kineticenergies and formation times of secondary ions have been investigated. The results suggestdelayed (10-10-10-9s) formation of target-specific ions in the gas phase. A concept ofexothermic matrices has been tested experimentally. A new effective matrix for peptides andproteins, HMX, has been found. In the keV-atomic-ion mode, target-specific ions are foundto possess kinetic energy distributions that are characteristic for gas-phase ion formation. Thissuggests that the ion-formation mechanisms may be similar in both MeV and keV modes.Polyatomic ion-induced desorption has been studied using multiply-charged proteinprojectiles. The total negative ion yield is found to depend primarily on the surface density ofthe deposited energy. The utility of these findings for mass determination of mixturecomponents from complicated electrospray-ionization spectra is demonstrated.