In QIT mass spectrometry when automatic
gain control is active a prescan preceeds every analytical scan to
determine the proper analytical ion injection time. It consists of a
short (<10 ms) ion injection to determine the ion current.
In atomic emission spectrometry with CCD/CID detection systems with limited linear working range a prescan preceeds every analytical measurement to determine the proper exposure time for every channel in order to stay within the upper electron capacity of the detector element.
The term "prescan" was found in the following pages: