Soft depth-profiling of mixed peptide/lipid samples by means of cluster induced desorption/ionization mass spectrometry-High depth resolution and low matrix effect.

Abstract

Mixed peptide/lipid samples were analyzed with respect to their chemical composition by means of desorption/ionization induced by neutral SO2 clusters (DINeC) in combination with mass spectrometry (MS). Depth profiles of the mixed films indicated a segregation layer of lipid on top of all samples. The thickness of this layer as obtained by DINeC-MS was in the order of one nanometer what can be seen as an upper limit for the depth resolution of DINeC-MS. The relative amounts of the substance of peptide and lipid derived for the bulk material of mixed samples with different compositions were found to be close to the nominal values indicating a low matrix effect. Throughout the depth profiles, only intact molecular ions [M+H]+ as well as dimers of peptides and lipids were detectable, indicating the soft nature of DINeC even when used for depth profiling of biomolecular samples.