Characterisation and ionisation modelling of matrices in MALDI mass spectrometry

Allwood, Daniel Anthony

Abstract

Experimental investigation of several matrix molecules commonly used in matrix- assisted laser desorption/ionisation (MALDI) mass spectrometry has provided the basis for modelling matrix ionisation within MALDI. Improvements in sample preparation, and in particular the formation of optically thin matrix films by sublimation-deposition, have made possible the optical characterisation of MALDI matrix molecules. These investigations have yielded estimates of several molecular photophysical parameters relevant to MALDI, e g. ground state absorption coefficient, a, fluorescence decay rates and fluorescence quantum efficiencies. Furthermore, the strong relationship between a and the degree of matrix ionisation observed due to pulsed laser irradiation has been demonstrated. Based on this information an excited-state ionisation model has been developed wherein a two-photon excited state o f the molecule draws upon its vibrational energy to undergo thermal ionisation. Ionisation is assumed to occur within the laser- desorbed gas-phase plume, which provides rapid (ps) thermal equilibration o f vibrational energy, and within the laser pulse duration itself. Predictions of this model show excellent agreement with experiment both in terms o f the strong power scaling with laser fluence F (~F10) and in the total ion yield (^lO-6) and suggests this ionisation route as a plausible alternative to multiple photon ionisation, It is hoped that the matrix photophysical data and ionisation modelling will enable further theoretical treatment of various aspects of MALDI and that the better understanding lent to the subject will ultimately result in improved experimental practise.

Citation

Allwood, D. A. Characterisation and ionisation modelling of matrices in MALDI mass spectrometry. (Thesis). University of Hull. https://hull-repository.worktribe.com/output/4223836

• Thesis Type: Thesis
• Deposit Date: Jan 17, 2022
• Publicly Available Date: Feb 24, 2023
• Keywords: Physics
• Public URL: https://hull-repository.worktribe.com/output/4223836
• Additional Information: Department of Physics, The University of Hull
• Award Date: Apr 1, 1998