Another approach to analyse proteomes without gels is "shotgun" analysis using MudPIT [136] . In the MudPIT approach, protein samples are subject to sequencespecific enzymatic digestion, usually with trypsin and endoproteinase lysC, and the resultant peptide mixtures are separated by strong cation exchange (SCX) and reversed phase (RP) high performance liquid chromatography (HPLC) [137, 138] . Peptides from the RP column enter the mass spectrometer and MS data is used to search the protein databases [138] . The MudPIT technique generates an exhaustive list of proteins present in a particular protein sample, it is fast and sensitive with good reproducibility however, it lacks the ability to provide quantitative information [139] [140] [141] . A combination of HPLC, liquid phase isoelectric focusing, and capillary electrophoresis provides other multimodular options for the separation of complex protein mixtures [142] .