What Is a Tandem Mass Spectrometer?

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  • Written By: Andrew Kirmayer
  • Edited By: Shereen Skola
  • Last Modified Date: 17 October 2019
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A mass spectrometer is an instrument often used to measure the mass of molecules, which can help identify the compounds in a sample. Charged particles called ions are released from the sample and analyzed. An instrument with multiple analyzers is called a tandem mass spectrometer (MS/MS). Typically able to fragment molecules and ions, it is often used to identify proteins and other organic substances. The instrument can include spectrometers of a single type or combine several of them; two, three, or four analyzers are sometimes incorporated.

One type of molecule or protein can be isolated by a magnetic field in a tandem mass spectrometer. The first analyzer can be used to accomplish this. Ions are often stabilized by a second analyzer before the molecules are exposed to a gas. Collisions at the molecular level cause the particles to break into fragments, which are detected by a third analyzer. While there are several methods for fragmenting molecules, sometimes one analyzer can be used with a quadrupole ion trap, which exposes ions to electrical fields and ejects them from a radio frequency field.


The detector of a tandem mass spectrometer typically tracks ionic activity. It then creates a signal that is sent to a computer system that stores the data. A graphical plot is generally used to indicate what is in the sample and what the molecular mass of each substance is. The plot can also show the amount of each type of molecule or protein in the sample. There are various types of detectors that can be used in an MS/MS, which include photomultipliers, designed to detect electromagnetic energy, or electron multipliers, which are vacuum tubes that collide electrons to amplify current.

Different types of experiments can be performed with a tandem mass spectrometer. A common one typically is single mass monitoring, in which the first analyzer allows on type of particle through, while the second looks for a specific fragment. Multiple reaction monitoring involves the tracking of different types of ion fragments by the second analyzer. These are both often used in pharmaceutical studies, while precursor ion scan experiments generally help detect ion losses and detect molecular components that are unknown.

The tandem mass spectrometer can also be used as a metabolic screening tool. It has been used to find newborn disorders related to proteins called amino acids. Blood, thyroid, and metabolic conditions can be detected by analyzing blood samples with an MS/MS in laboratories.


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