Question

Explain what are the differences between ‘‘SCAN’’ and ‘‘SIM’’ in GC-MS. Why ‘‘SIM’’ is needed to achieve high sensitivity and lower detection limit?

Answer 1

Gas chromatography mass spectrometry is performed on the mixture of gases liquids or solids.

GC-MS can be carried out either in SCAN mode or in SIM mode or selected ion monitoring mode. The mode is decided based on the aim of the analysis.

If the sample components are identified using mass spectrum, then SCAN mode is necessary.

For quantitative analysis of trace components SIM mode is used, because lower detection limits can be obtained with the SIM mode than the SCAN mode for quantitative analysis, because the sensitivity is tens to hundred times more precise in SIM mode.

In SIM mode while single ion is detected, all the other ions having target m/z will reach the detector. The difference in sensitivity depends on a mass range of scan, number of ions monitored in SIM and the relative abundance of the monitored ion.