title: Quantitative preparative gas chromatography of caffeine with nuclear magnetic resonance spectroscopy.
abstract: Caffeine test solute was employed in combination with an internal standard (IS), 1,4-dimethoxybenzene, in preparative-gas chromatography (prep-GC), with nuclear magnetic resonance (NMR) experiments. The IS served to: (i) quantify the trapping efficiency of an external trapping assembly, consisting of a capillary column cryotrap at the end of the analytical column; (ii) quantify the solute response in different NMR samples; and (iii) permit correlation of expected level of response of a compound in the NMR experiment, based on relative responses of the IS and solute in the GC result. The recovery rate of caffeine from multiple injections of sample (1×, 2×, 5× and 10×) was 69.6 ± 1.3%, which correlated well (R(2) = 0.999) with the number of injections of compound. The (1)H-NMR spectrum was sufficient to enable structural characterisation of the reference caffeine compound, and was achieved with recovery of amounts of ≤10 μg from a single aliquot. Less than 400 μg of collected caffeine (40 replicate injections) was sufficient for structural characterisation by (13)C-NMR spectral analysis. The method allows development of approaches to separate unknown compounds in complex samples, and to separately use MS and NMR for their characterisation.
authors.affiliation: Australian Centre for Research on Separation Science, School of Chemistry, Monash University, Clayton, VIC, Australia.
authors.forename: Leesun
authors.initials: L
authors.lastname: Kim
authors.forename: Blagoj
authors.initials: B
authors.lastname: Mitrevski
authors.forename: Kellie L
authors.initials: KL
authors.lastname: Tuck
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Marriott
mesh_terms: D002110:Caffeine / Q000032:analysis*; D002849:Chromatography, Gas / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*
chemical_list: D002110:Caffeine