Hyphenated techniques in multidimensional gas chromatography for analysis of wine aroma and related odorants

The advent of analytical multidimensional gas chromatography (MDGC) techniques, with recent development in comprehensive two-dimensional gas chromatography (GC×GC) as well as microfluidic technology in conventional heart-cut MDGC, has achieved excellent separation efficiency for advanced characterization of complex volatile and semi-volatile samples, which is unlikely to be accomplished by single dimensional chromatography. This dissertation work has highlighted the potential opportunities for continued innovation in multidimensional applications, including its compatibility with detection systems of dual channel flame photometric detection (FPD) and olfactometry, as well as alternative operational modes for various GC×GC and MDGC arrangements for analysis of wine and related odorants. Observation of GC×GC-FPD performance in the analysis of sulfur- (S) and phosphorus- (P) containing compounds suggests the appropriate detector flow, including hydrogen, air and nitrogen gas to achieve the maximum response and peak symmetry with adequate data sampling rate. Separation of sulfur-containing organophosphorus (OP) pesticides in S2 and HPO modes, as well as the organosulfur (OS) compounds in diesel and kerosene samples in S2 mode has been demonstrated. Volatile constituents in wine and brewed coffee were investigated using a combined system incorporating both GC-olfactometry (GC-O) and GC×GC-flame ionisation detection (GC×GC-FID). GC×GC allowed resolution of co-eluting compounds which coincided with the odour region located using GC-O, whilst the character-impact odorants were tentatively identified through data correlation of GC×GC contour plots across results obtained using GC×GC-ToFMS and GC×GC-FPD. An on-line enrichment of injected compounds in MDGC approach was presented here by performing multiple injections of a sample, selected compounds or regions of a primary column separation, which can be collected in an internal cryotrap using a well pressure-balanced microfluidic heart-cut device. Re-mobilising the trapped species then allows elution and further resolution on the secondary column. Peak areas of the re-mobilised compound correlate well with the number of sample injections (up to 50 replicate injections tested), showing the method is suited to quantitative trapping of alkanes of mass greater than about dodecane, and fatty acid methyl esters (FAMEs) greater than the C8 homologue. The method was applied to peppermint oil (menthol as major component of 44%) and lavender oil (α-terpineol and neryl acetate as minor components of 1.05 and 0.42% abundance), which gave good areas and height correlations, whilst good recovery around 90% was observed for menthol compounds with a total recovery up to 10s of μg. A simple and effective way for improving sensitivity and selectivity of solid phase microextraction (SPME) sampling has been demonstrated by coupling multiple SPME sampling and cryotrapping events for wine headspace in GC-O analysis. By performing multiple SPME sampling employing different chemical polymer coatings, desorbed solute from the integrated sampling is accumulated by the internal cryotrap (CT) prior to 1D chromatographic analysis. Apolar alkane volatiles of mass greater than nonane, and most polar alcohols, including methanol are retained in this approach. Chromatographic signals eluting later than the ethanol peak during wine analysis were found to progressively increase in response, and correlated well with the cumulative number of SPME samplings. Accumulation in the CT of volatile solutes derived from up to 12 repeat SPME sampling events has been demonstrated, revealing similar pattern but higher detection response of aromagram as compared to that by single fibre sampling. The final stage of the dissertation study describes an integrated system having the combined capability to perform GC, GC×GC, and MDGC using olfactometry (O), FID, and/or mass spectrometry (MS) detection. A number of contemporary GC methods incorporated into a single instrument provides initial assessment of volatile compound composition through GC×GC-FID, which can be correlated with GC analysis using parallel O and FID detection, followed by subsequent microfluidic H/C of the chromatographic elution from the first dimension (1D) column for further resolution on a long second dimension (2DL) column for parallel detection of O and MS. An analytical strategy that incorporates GC-FID/O, GC×GC-FID, and MDGC-MS/O analyses with cumulative SPME sampling for volatile sample enrichment is presented in this work. Excellent qualitative and quantitative performance was demonstrated with a Shiraz wine sample and an allergens mixture. A novel approach to obtain 2D retention indices has been also introduced, allowing matching of mass spectral, retention indices in 1D and 2D data for reliable identification of unknown odorant compound. These novel hyphenated approaches present highly efficient analytical capability, which permit enhanced separation and identification power for many more components in a complex sample.