# How Mass Spectrometry Works

By: William Harris

## Deflection and Detection of Ions HowStuffWorks

­­­­­­­C­reating and accelerating ions are essentially preparatory steps to the real work of mass spectrometry -- mass analysis. The main job of the mass analyzer is to apply an external magnetic field to the ions exiting the ionization chamber. This external field interacts with the magnetic field generated by the fast-moving particles, causing the path of each particle to bend slightly. How much an ion's path curves depends on two factors: the mass of the ion and its charge. Lighter ions and ions with a greater charge are deflected more than heavier ions and ions with a smaller charge.

Chemists combine these two variables into a value called the mass-to-charge ratio, which is represented mathematically as m/z (or m/e). For example, if an ion has a mass of 18 units and a charge of 1+, its m/z value is 18. If an ion has a mass of 36 units and a 2+ charge, its m/z value is also 18. Most of the ions moving from the ionization chamber to the mass analyzer have lost a single electron, so they have a charge of 1+. That means the m/z value of most ions passing through a mass spectrometer is the same as the mass of the ion.