Low resolution mass spectrometryshows the m/z ratio or mass-to-charge ratio of each isotope and the corresponding percentage abundances.Different isotopes are detected separately because they have different masses.The relative heights of the peak gives the relative abundances and the m/z ratio of a single charged ion gives the relative mass of the isotope.High resolution mass spectrometry can measure mass accurately to 5d.p. e.g. an atom of 12C has a mass of 12.00000 atomic mass units and an atom of 16O has a mass of 15.9949u.Low resolution mass spectrometry gives the m/z to the nearest whole number and may not be enough to distinguish between two molecules having the same molecular mass to the nearest whole number.