By Peak-Matching Methods

Therefore, for accurate mass measurement, a standard mass peak (M,) is selected, and the accelerating voltage (V) is changed until the sample ion peak (M ) exactly coincides with the position of Mj. This technique is called peak matching, and the ratio between the original and new voltages (VA ) multiplied by mass (Mj) gives the unknown mass, M . 

For greatest accuracy, the standard mass (M,) should be as close as possible to the unknown (M ). 

Peak matching can be done on quadrupole and magnetic-sector mass spectrometers, but only the latter, particularly as double-focusing instruments, have sufficiently high resolution for the technique to be useful at high mass. 

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