How are tandem mass spectrometers used?

Tandem mass spectrometers are used to identify and quantify molecules in a sample by analysing their mass and charge.

Tandem mass spectrometry, often abbreviated as MS/MS, is a powerful analytical tool used in many scientific fields, including chemistry, biochemistry, and pharmacology. It involves two stages of mass spectrometry, hence the term 'tandem'. The first stage, known as the 'parent' stage, ionises molecules in a sample and separates them based on their mass-to-charge ratio. The second stage, the 'daughter' stage, further fragments these ions and analyses their mass-to-charge ratio. This two-step process allows for a more detailed analysis of the sample, providing information about the structure and identity of the molecules present.

The process begins by introducing the sample into the spectrometer, where it is ionised, typically by a process such as electrospray ionisation or matrix-assisted laser desorption/ionisation. The ions produced are then accelerated into the first mass analyser. This device uses an electric or magnetic field to separate the ions based on their mass-to-charge ratio. The ions of interest, known as 'precursor' ions, are selected and passed into a collision cell.

In the collision cell, the precursor ions are fragmented into smaller 'product' ions. This is achieved by colliding the precursor ions with a gas, such as helium or argon. The resulting product ions are then analysed in the second mass analyser, again based on their mass-to-charge ratio. The resulting data can be used to determine the structure of the original molecule, as the pattern of fragmentation can provide clues about the arrangement of atoms within the molecule.

Tandem mass spectrometry is particularly useful in identifying and quantifying molecules in complex mixtures, as it can distinguish between molecules with similar mass-to-charge ratios. It is also highly sensitive, capable of detecting even trace amounts of a substance within a sample. This makes it a valuable tool in fields such as drug discovery, where it is used to identify potential drug candidates, and environmental science, where it is used to detect pollutants in air or water samples.