Abstract
The peak widths and relative intensities of the singly- and multiply-charged molecular ions appearing in plasma desorption mass spectra are used as a probe for the stability of molecular ions. Two peptides, lysozyme and lactalbumin, which have similar molecular weights and tertiary structures, but different primary structures and isoelectric points, were prepared in solutions of different pH, before adsorption to nitrocellulose foils. The peak widths of the resultant molecular ion signals were minimized near their respective isoelectric points, which is consistent with reports on the stability of their tertiary structures and/or enzymatic activities near the isoelectric point. Similar studies were carried out with the addition of glutathione, a matrix which has effects on PDMS spectra similar to that of the nitrocellulose surface.
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