Matrix Clusters, Polymer-Matrix Adducts, and Cation Attachment Mechanisms in the MALDI Analysis of Polystyrene

Published

October 16, 2008

Author(s)

R J. Goldschmidt, William R. Blair, Kathleen M. Flynn, Anthony A. Giuseppetti

Abstract

In the analysis of polystyrene by matrix-assisted laser desorption/ionization (MALDI), matrix clusters, polymer-matrix adducts, and polystyrene oligomers are all ionized by attachment of metal cations. Matrix clusters compete for cations with polystyrene and may also play a role in the mechanism of cation attachment to polystyrene. It has been shown by post-source decay (PSD) experiments that decay of polymer-matrix adducts plays a role in the production of cationized polystyrene ions. The formation of matrix cluster ions and of polymer-matrix adduct ions was investigated using layered sample preparations. Two methods were used to prepare layered samples. In the first method, an aqueous silver or copper salt solution was deposited on top of a dried polystyrene-matrix layer. Since neither polymer nor matrix are soluble in water, there is little or no opportunity for solution phase chemistry to occur between the metal and the polymer or matrix. In the second method, electrospray sample deposition was used to deposit separate layers. Scanning electron microscopy (SEM) indicates that electrosprayed droplets arrive at the MALDI target dry or virtually dry, and so again there is little or no opportunity for solution phase chemistry to occur between species in the separate layers. Experiments in which a salt layer was deposited on top of a polymer-matrix layer indicated that matrix salt formation and cation attachment to polystyrene and to matrix species readily occur without solution phase interactions. Experiments in which a second matrix layer was deposited on top of a polymer-matrix-salt layer indicated that matrix clusters and polymer-matrix adducts are also readily formed without solution phase interactions. Some differences exist between mass spectra obtained from layered and non-layered samples, so some contribution from directly desorbed species is not ruled out. However, interactions occurring during expansion of material from the sample subsequent to the laser pulse clearly can make a significant contribution to the formation of species observed in MALDI mass spectra.

Citation

Journal of the American Society for Mass Spectrometry

Pub Type

Journals

Keywords

adduct formation, cation attachment, cluster formation, ionization mechanisms, layered samples, MALDI, polystyrene, scanning electron microscopy

Citation

Goldschmidt, R. , Blair, W. , Flynn, K. and Giuseppetti, A. (2008), Matrix Clusters, Polymer-Matrix Adducts, and Cation Attachment Mechanisms in the MALDI Analysis of Polystyrene, Journal of the American Society for Mass Spectrometry (Accessed December 13, 2024)