Multidimensional analysis (MDA) certainly has been done for a long time! Many people are, to a lesser or greater degree,experienced in MDA. By MDA, we mean hyphenated chemical analysis combining two distinct techniques that themselves are bona fide analysis methods. The most recognizable MDA technique is gas chromatography–mass spectrometry (GC –MS)—combining dimensions of GC, which generates a sequence of time-resolved components and potentially constitutes molecular speciation, with a mass spectrum that provides some measure of molecular specificity by virtue of the mass fragmentation pattern of a molecule. By all accounts, GC–MS operates reliably, reproducibly, and sensitively for components detected by MS, for a sample that is resolved into chemical components by GC . Without further information, GC lacks molecular specificity, sinc eit just gives the recognized peak response to each compound in a sample. If we can assign each response to a specific compound,then GC provides reliable molecular information. Thus, GC–MS is used as both a screening and target analysis method — we get a snapshot of the total sample or we can analyze a subset of compounds.