An Introduction to Mass Spectrometry (cont.)

II. Mass Analyzer & Ion Detector

Once ions are created, individual mass-to-charge ratios (m/z) are separated by a second device, a mass analyzer, and transferred to the third device, an ion detector. A mass analyzer uses some physical property (e.g., electric or magnetic fields or time of flight) to separate ions of a particular m/z value, which then strike the ion detector. The magnitude of the current produced at the detector as a function of time (e.g., the physical field in the mass analyzer is changed as a function of time or the time it takes the ion to move a certain distance) is used to determine the m/z value of the ion. This figure shows an ion trap mass spectrometer with ions trapped in the electric field.

By changing the characteristics of the field, ions can be manipulated

and ejected from the trap to a detector. The time component as a function of the field is what determines the m/z value of the ions.

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