In the selected ion monitoring (SIM) mode, the MS detector monitors a limited number of m/z values that are characteristic of a targeted compound or compounds. During an analytical run, the mass analyzer repeatedly switches between the selected m/z values and monitors each m/z value for a programmed dwell time before averaging the measured ion intensities and moving on to the next value.

SIM generates mass chromatograms of only the monitored m/z values, not complete mass spectra like those generated in full-scan mode.

NOTE

Without a complete mass spectrum, you cannot perform a library search to identify an unknown compound.

SIM is ideally suited for trace analysis and offers reduced file sizes compared to full-scan operation because SIM records only the information of interest.