CHAPTER 5: Light as an Ionizing Agent in Mass Spectrometry. Microbial Identification by Matrix Assisted Laser Desorption Ionization–Mass Spectrometry Check Access

Light is an important tool in the hands of mass spectrometrists and forensic chemists that are interested in the accurate identification of the unknown. As a matter of fact, lights is the key to some fundamental ionization techniques. Atmospheric pressure photoionization (APPI) is a relatively new ionization method for liquid chromatography-mass spectrometry (LC-MS) which exploits light to ionize gaseous analytes through gas-phase reactions. APPI makes it possible to analyze by LC-MS compounds that would not be ionized by other athmospheric pressure ionization mechanisms, as polyaromatic hydrocarbons, that poses challenges to public health, or drug metabolites in biologicla fluids. Light was again necessary for the brilliant development of matrix assisted laser desorption/ionization (MALDI) technique. One of the main success of MALDI-MS is the identification of proteins and protein digests that made it an indispensable tool in the proteomic field. For the identification of unknown bacterial species, the protein profiling of whole bacterial cells is achieved rapidly and efficiently by MALDI-MS and applications will be presented in the frame of epidemiological surveillance, i.e. the recognition of early incidents, the analysis of cross-transmission, and the monitoring of treatment programs.