Introduction of Mass spectrometry and identification of microorganism

Mass spectrometry is an analytical technique that determines molecule masses extremely accurately. Nowadays many different mass spectrometer implementations are used. All of them contain three components:

  1. Ion source: converts a portion of the sample into ions and gives them a mass-to-charge dependent trajectory.
  2. Mass analyzer: sorts the ions by their trajectory.
  3. Detector: measures an indicator quantity for the presence of the ions, thus enabling the determination of the abundance of each ion present.

Depending on the phase of the sample (gas, fluid, solid) different methods are used to ionize the material, ranging from electron ionization for gases and vapors to electrospray and matrix-assisted laser desorption ionization (MALDI) for fluids and solids.

While the different implementations of mass spectrometry have proved extremely useful in analytic chemistry, analysis of organic samples has appeared troublesome. Large molecules such as proteins and peptides tend to disintegrate during the process, hence losing their m/z information.

To prevent disintegration of the sample molecules, in the 1980‘s Karas & Hillenkamp and Tanaka et al. developed a ‘soft’ ionization technique, matrix-assisted laser desorption ionization (MALDI). Key element in this technique is that the sample material is covered by an easily ionizable ‘matrix material’.

By combining the MALDI technique with a Time-of-Flight (TOF) mass spectrometer and applying it to (microbial) cells, part of the peptides, proteins and other elements contained in the cell become visible as peaks in the mass spectrum.

Today MALDI-TOF is widely used for species determination of bacteria and fungi in routine microbiological laboratories.