selected ion monitoring

Selected ion monitoring (SIM) is the practice of monitoring and  recording ion currents at one or more selected ion m/z values  with time, rather than recording full mass spectra, as sample  is introduced into the ion source. Because the detector is integrating signal for a longer time at the relevant ion, limits of  detection can be lowered, albeit at a cost of susceptibility of  the experiment to unexpected interferences. Use of the terms  multiple ion detection, multiple ion (peak) monitoring, and  mass fragmentography have also been used but are discouraged. The terms single ion monitoring or multiple ion monitoring are sometimes used.