Online coupling of enantioselective capillary gas chromatography with proton nuclear magnetic resonance spectroscopy

Abstract

The hyphenation of enantioselective capillary gas chromatography and mass spectrometry is not always sufficient to distinguish between structural isomers, thus requiring peak identification by NMR spectroscopy. Here the first online coupling of enantioselective capillary gas chromatography with proton nuclear resonance spectroscopy is described for the unfunctionalized chiral alkane 2,4-dimethylhexane resolved on octakis(6-O-methyl-2,3-di-O-pentyl)-gamma-cyclodextrin at 60 degrees C. NMR allows constitutional and configurational isomers (diastereomers and enantiomers) to be distinguished. Enantiomers display identical spectra at different retention times, which enable an indirect identification of these unfunctionalized alkanes. The presented method is still at an early development stage, and will require instrumental optimization in the future.

Molecular spectroscopy – Information rich detection for gas chromatography

“…for volatile model compounds dichloromethane, tetrahydrofuran, acetone, and diethyl ether, using continuous-flow solenoid micro-coil 1 H NMR measurements at 400Hz [84], and for separation of stereoisomers and enantiomers of cis-and trans-1,2-dimethylcyclohexane [75] as well as investigations using enantioselective GC separation of racemic 2,4-dimethylhexane whose enantiomers showed identical NMR spectra but different retention times [85].…”

A Review of Analytical Techniques and Their Application in Disease Diagnosis in Breathomics and Salivaomics Research

“…NMR allows constitutional and configurational isomers to be distinguished but, while semi-preparative GC is an excellent technique for isolating small amounts of volatile compounds from mixtures such as breath, the recording of the NMR spectra of gases leaving a gas chromatograph which contain only trace amount of analytes imposes some problems in terms of sensitivity. Online coupling of GC with NMR has nevertheless been described for the analysis of volatile stereoisomers [ 81 , 82 ], caffeine [ 83 ], and menthol and menthone from peppermint oil [ 84 ]. Gas phase NMR is thus possible, although far too complex for regular use but further developments in this field are still highly desirable for breath analysis.…”

Pharmaceutical impurities and degradation products: Uses and applications of NMR techniques

“…To date, CE-NMR is not a well-established method; however, development of smaller volume NMR probes and continuous enhancements of NMR sensitivity will probably transform CE-NMR in the near future into a valuable technique for biopharmaceutical analysis. On the other hand, despite its years of evolution and recent advances, GC-NMR is still in its infancy [79]; even more, its sensitivity, interfacing and other instrumental details require strong improvements.…”