Development of ²⁵²Cf plasma desorption mass spectrometry for high molecular weight protein analysis

Abstract

Studies were undertaken in instrumentation and methodology to advance the capability of [252]Cf-PDMS for high molecular weight protein analysis. Instrumentation was developed to reduce the background in [252]Cf-PDMS spectra without significant loss of ion yield or loss of mass accuracy. This instrumentation included the use of an electrostatic particle guide as a particle deflector in both a static and pulsed mode, and the use of a large area secondary i ion detector of a novel design. Methodological development was focussed on the study of the role of the matrix in 252Cf-PDMS. New small molecule substrates were introduced for use as matrices with proteins in [252]Cf-PDMS. Experimental investigations were carried out to determine the influence of different substrate/matrices on protein molecular ion yield, background and resolution. Optimal protein target preparation conditions were determined for selected substrates by studying the influence of substrate parameters, including substrate thickness, and adsorbate volume and concentration. The performances of the small molecule matrices were compared to that of nitrocellulose, a polymer matrix commonly used for protein analysis in [252]Cf-PDMS. The role of surface functionality of the substrates was found to be an important factor. Only those substrates containing acidic protons produced high quality protein spectra. A radio-assay was performed to determine the quantity of protein adsorbed by the different substrates. Initial kinetic energy measurements of ions desorbed from various selected matrices revealed that cooler ions are produced from the small molecule matrices. The influence of the matrix molecules on the desorption of proteins was further investigated by examining the ion yields as a function of time for a volatile matrix. Findings from the substrate investigations were used to clarify the desorption process and to establish guidelines for matrix selection for high mass proteins in [252]Cf-PDMS.