Modern mass spectrometer design

As mentioned in an earlier article, J. J. Thomson constructed one of the earliest mass spectrometers and conducted the well-known experiment to determine the mass-to-charge ratio of an electron. Since then, different mass spectrometer designs have been developed, with a typical modern Thermal Ionisation mass spectrometer (TIMS) consisting of the following:

    • Ioniser where the sample to be analysed is bombarded by electrons to form ions and ion fragments, which are then accelerated into the mass analyser.
    • Mass analyser that utilises a magnetic field to deflect and separate the ions according to their mass-to-charge ratios (u/z). Note that the mass-to-charge ratios before the 1980s were quoted in u/e where e is the charge of an electron instead the number of charges, which is z.
    • Detector that measures the abundance of ions with reference to their mass-to-charge ratios and converts the data into electrical signals.

The result is a plot of ion abundance versus mass-to-charge ratio, with the height of the peaks normalised to the most abundant ion in the spectrum.


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