What is the mass-to-charge ratio scale and what are multiply charged ions?
The mass-to-charge ratio (m/z) of an ion is simply its mass (in mass units, Daltons or ‘Da’) divide by its charge (in charge units). Do not use SI units of mass and charge to calculate this ratio! The mass-to-charge ratio is usually on the x-axis of a mass spectrum and is usually indicated by either ‘m/z’, ‘m/e’ or ‘Da/e’. Example: A molecule of phenol has a formula C6H6O and therefore a mass of 94 mass units (O=16, C=12 and H=1). If it holds a single charge by loss of one electron it will have a mass to charge ratio of 94/1 = 94. If it holds a single charge by protonation (gaining of H+) it will have a mass to charge ratio of (94+1)/1 = 95. It is also possible to have multiply charged ions in your mass spectrum, especially with electrospray ionisation and MALDI (see later). In these cases your mass-to-charge ratio will be lower than the mass because the charge is greater than 1. Example: A molecule of the protein myoglobin has a mass of 16,950 Da.
The mass-to-charge ratio (m/z) of an ion is simply its mass (in mass units, Daltons or ‘Da’) divide by its charge (in charge units). Do not use SI units of mass and charge to calculate this ratio! The mass-to-charge ratio is usually on the x-axis of a mass spectrum and is usually indicated by either ‘m/z’, ‘m/e’ or ‘Da/e’. Example: A molecule of phenol has a formula C6H6O and therefore a mass of 94 mass units (O=16, C=12 and H=1). If it holds a single charge by loss of one electron it will have a mass to charge ratio of 94/1 = 94. If it holds a single charge by protonation (gaining of H+) it will have a mass to charge ratio of (94+1)/1 = 95. It is also possible to have multiply charged ions in your mass spectrum, especially with electrospray ionisation and MALDI (see later). In these cases your mass-to-charge ratio will be lower than the mass because the charge is greater than 1. Example: A molecule of the protein myoglobin has a mass of 16,950 Da. When ionised by electrospray ionisati
