What is a mass spectrometer?
A mass spectrometer (MS) is an instrument that measures the mass
(more accurately: the mass/charge) of charged atoms and molecules. It uses
electric and magnetic fields to accomplish this. So roughly speaking it
is a scale for atoms.
What are mass spectrometers used for?
Mass spectrometers are used for chemical and biological analysis.
Why is it called a "mass spectrometer"?
Good point. Since mass spectrometers actually measure mass/charge (m/Q) they would
correctly be called "mass/charge spectrometer". Now this sounds a bit clumsy.
Therefore the name "mass spectrometer" is fine.
One of the earliest mass spectrometer
was designed by J.J. Thomson. He named it the "parabola spectrograph" because all ions
with the same m/Q were on a parabola. His student F.W. Aston later designed a focusing
mass spectrometer where the ions no longer were on a parabola. Therefore he had
to come up with a new name. Even though Aston understood that his instrument was
measuring the m/Q of ions, he somehow failed to understand the real difference
between the quantity mass and the quantity mass/charge and called his instrument a "mass spectrograph."
This name was of course influenced by the optical spectrography that was done at that time.
Later, when the signals no longer were recorded on photographic plates,
the name was changed to "mass spectrometer."