When reading about how we can use a mass spectrometer in order to determine the mass of atoms/ions, several books that I have considered say that a mass spectrometer allows for a measurement of the mass-to-charge ratio of ions. Moreover, it is stated that the mass can be determined if the charge is known, but there is no more information on how this explicitly works.
How does the determination of the mass (not the mass-to-charge ratio) with a mass spectrometer work? Is the charge also determined? If not, which techniques are typically used in order to identify different isotopes when only having information about the mass-to-charge ratio?
Suitable references are also appreciated.