used application of the SID technique. For Ion-mobility mass spectrometry (IM-MS), SID is used for dissociation of the source activated precursors of three different types of protein complexes: C-reactive protein (CRP), transthyretin (TTR), and concanavalin A (Con A). This method is used to observe the unfolding degree for each of these complexes. For this observation, SID showed the precursor ions' structures that exist before the collision with the surface. IM-MS utilizes the SID as a direct measure of the conformation for each proteins' subunit. Fourier-transform ion cyclotron resonance (FTICR) are able to provide ultrahigh resolution and high mass accuracy to instruments that take mass measurements. These features make FTICR mass spectrometers a useful tool for a wide variety of applications such as several dissociation experiments such as collision-induced dissociation (CID, electron transfer dissociation (ETD), and others. In addition, surface-induced dissociation has been implemented with this instrument for the study of fundamental peptide fragmentation. Specifically, SID has been applied to the study of energetics and the kinetics of gas-phase fragmentation within an ICR instrument. This approach has been used to understand the gas-phase fragmentation of protonated peptides, odd-electron peptide ions, non-covalent ligand-peptide complexes, and ligated metal clusters. Quantitative proteomics Quantitative proteomics is used to determine the relative or absolute amount of proteins in a sample. Several quantitative proteomics methods are based on tandem mass spectrometry. MS/MS has become a benchmark procedure for the structural elucidation of complex biomolecules. One method commonly used for quantitative proteomics is isobaric tag labeling. Isobaric tag labeling enables simultaneous identification and quantification of proteins from multiple samples in a single analysis. To quantify proteins, peptides are labeled with chemical tags that have the same structure and nominal mass, but vary in the distribution of heavy isotopes in their structure. These tags, commonly referred to as tandem mass tags, are designed so that the mass tag is cleaved at a specific linker region upon higher-energy collisional-induced dissociation (HCD) during tandem mass spectrometry yielding reporter ions of different masses. Protein quantitation is accomplished by comparing the intensities of the reporter ions in the MS/MS spectra. Two commercially available isobaric tags are iTRAQ and TMT reagents. Isobaric tags for relative and absolute quantitation (iTRAQ) An isobaric tag for relative and absolute quantitation (iTRAQ) is a reagent for tandem mass spectrometry that is used to determine the amount of proteins from different sources in a single experiment. It uses stable