The present research reports the use of a three-dimensional preparative gas chromatography (prep GC) system, equipped with three Deans-switch devices and 5%diphenyl/wax/mid-polarity ionic liquid stationary phases, for the isolation of volatile components from a complex natural source, namely wampee essential oil (derived from Clausena lansium Skeels leaves). Collection was performed by using a simple and effective lab-constructed trapping device. Initially, an unknown (and abundant) wampee oil constituent was erroneously identified as α-sinensal, through an MS database search (a low similarity match was attained), performed after a GC-quadMS experiment., The unknown compound was then the isolated by using the novel prep GC system, in a highly pure form (at the mg level), and was correctly identified by using nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR) and mass spectrometry (MS). Both FTIR and MS data were used to confirm the NMR information. The name given to the molecule was (2E,6E)-2-methyl-6-(4-methylcyclohex-3-enylidene)hept-2-enal. The results herein described will demonstrate the need for a high-resolution GC step, prior to analyte collection, in the prep GC analysis of complex samples.