New ways in qualitative and quantitative protein analysis: Nano chromatography coupled to element mass spectrometry

The potential of inductively coupled plasma-mass spectrometry (ICP-MS), which allows element-specific detection of heteroelements (e.g. Se and S) incorporated in protein structures, is highlighted for sensitive qualitative and quantitative protein analysis. ICP-MS coupled to separation techniques such as size exclusion chromatography and gel electrophoresis (via laser ablation) can be employed at different steps in the proteomic workflow. Special emphasis is made on the couplings of capillary and nanoHPLC to ICP-MS that required the development of dedicated interfaces. Element-specific peptide mapping by nanoHPLC–ICP-MS has turned out to be a key technique in combination with peptide sequencing via nanoHPLC–electrospray MS. This could impressively be demonstrated for the identification of selenium-containing proteins in selenium-rich yeast. Furthermore the potential of sulfur isotope dilution analysis in nanoHPLC–ICP-MS is presented as generic tool for highly accurate, absolute protein quantification.