How is an atom’s mass measured?

The atomic mass of a specific atom or molecule is determined by using an experimental technique called mass spectrometry. This technique separates different isotopes of atoms to allow determination of the percent abundance or isotopic composition of the element in the given sample. Each isotope of the element appears as a peak in the mass spectrum. The intensity (height) of each peak depends on the abundance of that isotope in the sample and the unique location of the peak on the x-axis indicates the mass-tocharge ratio of the isotope. Knowing the charge on the isotope, we can calculate the mass of the isotope and from the relative abundance of different isotopes of the elements, the average relative atomic mass is calculated.