tandem mass spectrometry (MS/MS), a two-step technique used to analyze a sample for a predetermined set of substances, either by using a separate mass spectroscope for each step or by using the same spectroscope to perform the steps sequentially. In the first stage, a predetermined set of ions is selected for fragmentation; in the second, mass spectra are produced for the fragments. This technique is used in screening newborns for multiple metabolic disorders from a single blood sample.
