Method for Small-Molecule Discovery Based on Microscale-Preparative Multidimensional Gas Chromatography Isolation with Nuclear Magnetic Resonance Spectroscopy

Absolute chemical identification requires obtaining a pure compound followed by structure elucidation using spectroscopic techniques, principally NMR spectroscopy and mass spectrometry. Classical isolation techniques suffer from insufficient resolution for complex samples, requiring time-consuming fractionation in multiple steps. Here, a novel preparative technique based upon capillary column multidimensional gas chromatography (MDGC) with 2D NMR to resolve, isolate, and identify pure volatile components from a complex sample is described. As a model application, geraniol was isolated from an essential oil matrix using MDGC and quantitatively resolved from 15 partially coeluting compounds from the first column. Geraniol was recovered from 10 (8.6 μg) and 100 injections (77.6 μg; purity >99%) for subsequent NMR analysis at 500 and 800 MHz (with cryoprobe). Proton and gCOSY NMR experiments were successfully performed at 12.3 μg/mL (10 injections), while gHSQC and gHMBC NMR experiments were obtained at 110.8 μg/mL (100 injections). This approach is applicable to the biodiscovery of volatile molecular species or, indeed, any volatile compound in a complex matrix that requires confirmation of component identity.