SIM (Selected Ion Monitoring)

SIM is the Mass Spectrometer method used for recording an MS chromatogram at a specific mass. As only single ions are recorded with specific masses, the SIM mode is more sensitive than the Full-Scan mode. You can use up to 32 channels for data acquisition. These channels are called SIM_1 through SIM_32. In addition, one TIC channel is always recorded. The TIC channel summarizes the results of the single SIM channels.

With SIM chromatograms, the counts of specific masses (or more precisely, those with a particular mass-to-charge ratio) are added up. Thus, contrary to TIC chromatograms, SIM chromatograms contain data of a specific mass.

SIM chromatograms are always recorded during data acquisition. This is contrary to Mass Traces that are later extracted from Mass Spectra (see Using Mass Spectrometers  Extracting Mass Traces Afterward). If you record data in full-scan mode, you can later extract the SIM channel(s) as mass trace(s).

 Tip: 

The device methods of the aQa mass spectrometer (1.2) and the MSQ (1.3) are different. Therefore, please note the following difference: During data acquisition with the aQa mass spectrometer, data with the same mass range, polarity, and ionization voltage are always recorded in one channel. The Surveyor MSQ records them in different channels if the scan events are different for this data, i.e., if they are defined with different retention times. For example (same mass range, polarity, and ionization voltage):

Also, refer to How to …: Installing and Configuring Mass Spectrometers  Defining the Number of MS Channels in the Administrator Help section.