page_title: Tandem mass spectrometry
section_title: Tandem in time
hierarchical_section_title: Tandem mass spectrometry / Instrumentation / Tandem in time
caption_attribution_description: With the top cover removed, the ion trap itself and the detector dynodes can be seen in this shot from the front of the instrument.
context_page_description: Tandem mass spectrometry, also known as MS/MS or MS², is a technique in instrumental analysis where two or more mass analyzers are coupled together using an additional reaction step to increase their abilities to analyse chemical samples. A common use of tandem-MS is the analysis of biomolecules, such as proteins and peptides.
  The molecules of a given sample are ionized and the first spectrometer separates these ions by their mass-to-charge ratio. Ions of a particular m/z-ratio coming from MS1 are selected and then made to split into smaller fragment ions, e.g. by collision-induced dissociation, ion-molecule reaction, or photodissociation. These fragments are then introduced into the second mass spectrometer, which in turn separates the fragments by their m/z-ratio and detects them. The fragmentation step makes it possible to identify and separate ions that have very similar m/z-ratios in regular mass spectrometers.
context_section_description: By doing tandem mass spectrometry in time, the separation is accomplished with ions trapped in the same place, with multiple separation steps taking place over time. A quadrupole ion trap or Fourier transform ion cyclotron resonance (FTICR) instrument can be used for such an analysis. Trapping instruments can perform multiple steps of analysis, which is sometimes referred to as MSⁿ (MS to the n). Often the number of steps, n, is not indicated, but occasionally the value is specified; for example MS³ indicates three stages of separation.
  Tandem in time MS instruments do not use the modes described next, but typically collect all of the information from a precursor ion scan and a parent ion scan of the entire spectrum. Each instrumental configuration utilizes a unique mode of mass identification.
caption: An ion trap mass spectrometer is an example of a tandem mass spectrometry in time instrument.
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