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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.

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(a) It is assumed that the charge is e or a multiple of e. There is not a continuous range of charges as there is of masses.

(b) The means of producing the ions to be investigated (such as by electron bombardment) will usually produce many more ions with a single electronic charge than multiply charged ions.

(c) Generally we will know roughly the mass of ion that is being studied. Thus we would not interpret a reading as arising from (say) a doubly charged ion of twice the anticipated mass.

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  • $\begingroup$ Thank you for your answer. Just out of curiosity: Is it experimentally possible to determine the charge of those ions or is it just not feasible? $\endgroup$ – physicist23 Oct 11 '20 at 22:28

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