 This differs significantly from the extracted-ion chromatogram mentioned above in that only data for the ion(s) of interest are collected in a SIM experiment; for extracted-ion chromatograms, data for an entire mass range are collected during the run and then examined for analytes of interest after the completion of the run.The selected-reaction monitoring (SRM) experiment is very similar to the SIM experiment except that tandem mass spectrometry is used and a specific product ion of a specific parent ion is detected.The mass of the parent analyte is first selected while other ions are filtered away.