resolution of a mass spectrometer

The resolution of a mass spectrometer is defined in several different ways relative to the commonly given formula of m/Δm, where m is the mass of the ion at which resolution is specified. For two adjacent, symmetric peaks of equal height in a mass spectrum, the instrumental (physical or electrical) parameters are adjusted such that the peaks at masses m and (m -Δm) are separated by a valley that, at its lowest point, is just 10% of the height of either peak. Then, the resolution (10% valley definition) is m/Δm. The definition can be given also for 50% valley or 5% valley separations. For a single peak, the resolution is still calculated as m/Δm, but now Δm is the width of the peak at a height that is a specified fraction of the maximum peak height. A 5% peak width definition is technically equivalent to the 10% valley definition of resolution. A common standard is the definition of resolution based on Δm being the full width of the peak at half its maximum height (FWHM).