 Mass-to-charge ratio

The ratio of an ion's mass to its electric charge; in SI it has units $kg/C$. A convenient numerical mass spectrum coordinate is $x=(m/\mathrm{u})/z$, with $q=ze$ and positive integer $z$ here. This $x$ is dimensionless. Doubling $z$ at fixed mass halves $x$, so the electric charge state must be identified before assigning an isotope.

The mass-to-charge ratio (m/z) is a fundamental concept in mass spectrometry and ion physics. It is defined as the ratio of the mass (m) of an ion to its charge (z).