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There is an increasing trend of using ICP-MS as a tool in [[speciation analysis]], which normally involves a front end [[chromatograph]] separation and an [[elemental selective detector]], such as AAS and ICP-MS. For example, ICP-MS may be combined with [[size exclusion chromatography]] and quantitative preparative native continuous polyacrylamide gel electrophoresis ([[QPNC-PAGE]]) for identifying and quantifying native [[metalloprotein|metal cofactor containing proteins]] in biofluids. Also the phosphorylation status of proteins can be analyzed.
Recently{{When|date=June 2010}} a new type of protein tagging reagents called metal coded affinity tags (MeCAT) were introduced to label proteins quantitatively with metals, especially lanthanides.<ref name="pmid17627934">{{cite journal |author=Ahrends R, Pieper S, Kühn A, ''et al.'' |title=A metal-coded affinity tag approach to quantitative proteomics |journal= Molecular & Cellular Proteomics|volume= 6|issue= 11| pages = 1907|year=2007 |pmid=17627934 |doi=10.1074/mcp.}}</ref> The MeCAT labelling allows relative and absolute quantification of all kind of proteins or other biomolecules like peptides. MeCAT comprises a site-specific biomolecule tagging group with at least a strong chelate group which binds metals. The MeCAT labelled proteins can be accurately quantified by ICP-MS down to low attomol amount of analyte which is at least 2-3 orders of magnitude more sensitive than other mass spectrometry based quantification methods. By introducing several MeCAT labels to a biomolecule and further optimization of LC-ICP-MS detection limits in the [[Zepto-|zeptomol]] range are within the realms of possibility. By using different lanthanides MeCAT multiplexing can be used for [[pharmacokinetics]] of proteins and peptides or the analysis of the differential expression of proteins ([[proteomics]]) e.g. in biological fluids. Breakable PAGE [[SDS-PAGE]] (DPAGE, dissolvable PAGE), [[two-dimensional gel electrophoresis]] or [[chromatography]] is used for separation of MeCAT labelled proteins. Flow-injection ICP-MS analysis of protein bands or spots from DPAGE SDS-PAGE gels can be easily performed by dissolving the DPAGE gel after electrophoresis and staining of the gel. MeCAT labelled proteins are identified and relatively quantified on peptide level by MALDI-MS or ESI-MS.
==Sample introduction==
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