Investigations of Matrix Isolated, (UV) Laser Induced Polymer Sublimation Using a Time-of-Flight Mass Spectrometer

Abstract

The matrix isolated, laser induced polymer sublimation (also referred to as matrix assisted laser desorption) process for the production of gas phase protein ions was originally described phenomenologically by Karas and Hillenkamp [1]. A macromolecule of interest, e.g. a protein, was dissolved in a solution containing a large molar excess of nicotinic acid. This solution was dried to form a deposit on a metal substrate. The substrate was then placed into the ion source of a timfe-of-flight mass spectrometer and irradiated by a pulsed UV laser. The laser light was absorbed by the nicotinic acid “matrix” and then, by some process involving ablation of the matrix, protein molecules were expelled from the surface with one to three positive charges per peptide chain. Subsequent studies have demonstrated that a range of matrix molecules can produce the macromolecule sublimation effect [2], wavelengths other than 266 nm can be employed [3] and that the originally broad peaks demonstrated by Karas and Hillenkamp were caused by photochemically generated reactions that resulted in the addition of a variable number of matrix molecules to the protein [4]. Both positive and negative ions have been observed from this process [3,5]. Recently, it has been demonstrated that infra-red laser wavelengths can be used to produce a similar effect [6].