Orthogonal time-of-flight secondary ion mass spectrometric analysis of peptides using large gold clusters as primary ions.

Secondary ion mass spectrometry (SIMS) for biomolecular analysis is greatly enhanced by the instrumental combination of orthogonal extraction time-of-flight mass spectrometry with massive gold cluster primary ion bombardment. Precursor peptide molecular ion yield enhancements of 1000, and signal-to-noise improvements of up to 20, were measured by comparing SIMS spectra obtained using Au+ and massive Au4004+ cluster primary ion bombardment of neat films of the neuropeptide fragment dynorphin 1–7. Remarkably low damage cross-sections were also measured from dynorphin 1–7 and gramicidin S during prolonged bombardment with 40 keV Au4004+. For gramicidin S, the molecular ion yield increases slightly as a function of Au4004+ beam fluence up to at least 2 × 1013 Au4004+/cm2. This is in marked contrast to the rapid decrease observed when bombarding with ions such as Au5+ and Au9+. When gramicidin S is impinged with Au5+, the molecular ion yield decreases by a factor of 10 after a fluence of only 8 × 1012 ions/cm2. Comparison of these damage cross-sections implies that minimal surface damage occurs during prolonged Au4004+ bombardment. Several practical analytical implications are drawn from these observations. Copyright © 2004 John Wiley & Sons, Ltd.