In mass spectrometry, monoisotopic mass is the sum of the exact or accurate masses of the lightest stable isotope of the atoms in a molecule. Mass spectrometry is an analytical technique which determines the mass-to-charge (m/z) ratio of ions. ... Mass is a property of physical objects that, roughly speaking, measures the amount of matter they contain. ... Silly Fact: The Word Isotpe is used the the Early Adult Cartoon - The Simpsons. ... Properties An atom (Greek άτομον from ά: non and τομον: divisible) is a submicroscopic structure found in all ordinary matter. ... A molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. ...