[14] High resolution indicating better peak separation is also used in ion mobility spectrometry.
In this case, resolving power is defined as: The minimum peak separation ΔM which allows to distinguish two ion species is then called: Resolution and resolving power, when defined in this way, are consistent with IUPAC recommendations for microscopy, optical spectroscopy.
[19][20][21] There are several ways to define the minimum peak separation ΔM in mass spectrometry, therefore it is important to report the method used to determine mass resolution when reporting its value.
The valley definition defines ΔM as the closest spacing of two peaks of equal intensity with the valley (lowest value of signal) between them less than a specified fraction of the peak height.
The value obtained from a 5% peak width is roughly equivalent to a 10% valley.