The mass spectrum of an element shows a separate peak for each isotope. The horizontal axis shows the mass to charge ratio (m/z) and the vertical axis shows the relative abundance. For ions with a 1+ charge, the m/z value is equal to the relative isotopic mass.The relative atomic mass, Ar, is the weighted mean mass of an atom of an element compared with 1/12 of the mass of an atom of carbon-12. It is calculated from the mass spectrum using:Ar = Σ(m/z × relative abundance) ÷ Σ(relative abundance)If the abundances are given as percentages, the total is 100. If they are given as peak heights, divide by the sum of all the heights.The mass spectrum and calculation of the relative atomic mass of germanium are shown below. Germanium has five isotopes and its relative atomic mass is 72.632.
