Introduction to MS

Mass spectrometry (MS) can identify chemical composition of a sample based on the mass-to-charge ratio of charged particles. The instrument mainly contains three parts including ion source, mass analyzer and detector. The samples are ionized in the ion source using chemical or electron modes. Ions from the ion source were separated according to the m/z ratios in the analyzer part.
Two biological mass spectrometries were introduced during the lecture: Matix assisted laser desorption ionization (MALDI) and electrospray ionization (ESI). Both of them belong to soft ionization methods. The irradiated substance is embedded in crystallized matrix in MALDI. In contrast of MALDI, the ionization in ESI is achieved by spraying a solution into an electrical field. MS has been applied in many fields of protein research including protein identification, molecular weight determination, characterisation of post-translation modifications, relative quantification and also protein complex, etc.
It is important to note that the protein needs to be in solution without salts and detergents and should be purified before the MW measurement. For protein identification, the protein needs to be digested into peptide before analyzing by MS. The identification can base on peptide mass finger print (PMF) and MS/MS data from one or more peptides.