Metabolomics: The greatest omics of them all?
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Computational Biology↗
Biomedical subjects
Danielle Ryan
Publications and source records attributed to Danielle Ryan.
Studies on thermionic ionisation detection in comprehensive two-dimensional gas chromatography.
This study explores the application of specific thermionic ionisation detection in comprehensive 2-D GC (GC x GC) and represents the first report of GC x GC with nitrogen phosphorus detection (GC x GC-NPD). Of particular interest is the performance of the NPD with respect to peak parameters of asymmetry and sensitivity. Since GC x GC produces much narrower peaks than obtained with fast GC (e.g. 100 ms vs. <1 s) the effect of detector response time and any lack of symmetry arising from the detection step is important if peak separation (resolution) is to be maintained. It was observed that detector gas flows had a significant impact on peak asymmetry and peak magnitude, and that optimisation of the detector was critical, particularly for complex sample analysis by GC x GC-NPD. Peak asymmetries ranging from As = 1.8 to 8.0 were observed under different conditions of detector gas flows. Comparison of GC x GC-NPD with GC x GC-flame ionisation detection (FID) showed the former to be approximately 20 times more sensitive for the detection of nitrogen-containing methoxypyrazines analytes, and GC x GC-NPD had a larger linear detection range compared to GC x GC-FID. Furthermore, comparison of GC x GC-NPD and GC x GC-TOFMS chromatograms for the analysis of coffee head-space demonstrated the benefits of selective detection, ultimately realised in a comparatively simplified contour plot.
Journal Article↗
Orthogonality considerations in comprehensive two-dimensional gas chromatography.
This study explores separation orthogonality with respect to comprehensive two-dimensional gas chromatography (GC x GC) for a range of different column polarities in the first dimension (1D), with two second dimension (2D) column types. Systematic variation in the net polarity of the first dimension allows the effect of column phase relative polarity on analyte retention in both the first and second dimensions to be evaluated. First dimension polarity manipulation significantly affects elution temperature (T(e)) of the analytes. This alters the magnitude of retention on the second dimension, and the extent of utility of separation space. By use of retention factor/temperature data in single column experiments, along with 1D T(e) data, retention on the 2D column can be estimated. This allows the two-dimensional separation to be predicted, and compared with experimental data. Predicted GC x GC peak positions corresponded favourably with the experimentally derived chromatograms, yielding a simple approach for predicting two-dimensional separations, using unique column set combinations.
Chromatography, Gas↗
Analysis of strawberry volatiles using comprehensive two-dimensional gas chromatography with headspace solid-phase microextraction.
The aims of the current study were to develop an enantioselective multi-dimensional gas chromatography (GC x GC) method for the examination of strawberry volatiles and to use this method to make comparisons between the volatile profiles of different cultivars and between fresh picked and post-harvest berries of the same cultivar. Strawberry volatiles were sampled using solid-phase microextraction (SPME), and the repeatability and reproducibility of this method was examined. Semi-quantitative analysis of the volatiles was conducted using the relatively new technique of comprehensive multi-dimensional gas chromatography, using enantioselective (chiral) columns for the differentiation of analyte enantiomers. Chiral GC x GC facilitated the detection of key enantiomers in strawberry flavour. The (-)-enantiomer of 2,5-dimethyl-4-hydroxy-(2H)-furan-3-one (DMHF) and the S-enantiomer of linalool were tentatively identified as the predominant forms in both the cultivars Selva and Adina. The compounds benzaldehyde and methyl hexanoate were shown to decrease in post-harvest berries, whilst DMHF and nerolidol increased upon storage.
Chromatography, Gas↗
Analysis of methoxypyrazines in wine using headspace solid phase microextraction with isotope dilution and comprehensive two-dimensional gas chromatography.
This study reports an optimized headspace-solid phase microextraction (HS-SPME) method for the determination of methoxypyrazines in wine. Analysis was performed by using comprehensive two-dimensional gas chromatography with novel detection capabilities, including nitrogen phosphorus detection (GC x GC-NPD) and time-of-flight mass spectrometry (GC x GC-TOFMS). In the latter, stable isotope dilution was performed for the quantitation of 2-methoxy-3-(2-methylpropyl) pyrazine (IBMP), using labelled 2-(2H3)methoxy-3-(2-methylpropyl)pyrazine (d3-IBMP) as the internal standard, and resolution of the two analogues was facilitated using the deconvolution capabilities of the TOFMS. This research represents the first report of HS-SPME with isotope dilution and GC x GC-TOFMS (GC x GC-IDTOFMS). Analysis by GC x GC-NPD enabled detection limits of 0.5 ng/L for the quantitation of IBMP, which was superior to that obtained using GC x GC-IDTOFMS (1.95 ng/L). Nevertheless, both methods were adequately sensitive for real wine analysis, yielding highly comparable IBMP concentrations of 26.1 and 27.8 ng/L, respectively, from a Sauvignon blanc wine. The complexity of the real wine headspace was simplified as a result of selective detection using GC x GC-NPD and, in the case of GC x GC-IDTOFMS, the use of extracted ion chromatograms (EICs).
Chromatography, Gas↗
Analysis of roasted coffee bean volatiles by using comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry.
The volatile headspace from two coffee bean varieties, namely Arabica (Coffea arabica) and Robusta (Coffea canephora ex Froehner), were sampled by using solid-phase microextraction (SPME), and then analysed with comprehensive two-dimensional gas chromatography interfaced to a time-of-flight mass spectrometer (GC x GC-TOFMS). Two distinct column set combinations were investigated--an apolar-polar and polar-apolar configuration--and the separation achieved from each set was compared. Results were compared with a previous literature report for coffee analysed by GC x GC-FID, using an analogous polar-apolar column set combination, where authentic standards were used to confirm the position of the selected components in the 2D separation space. The present study provides independent mass spectral confirmation of component identity, and demonstrates that the relative, structured position of these components is comparable in the two experiments. Total ion current (TIC) chromatograms were processed using ChromaTOF automated data processing software. It was necessary to restrict the number of processed peaks to 1000 (S/N > 100), which required approximately 8 h for processing. Extracted ion chromatograms were generated using prominent fragment ions, and unique masses, to aid in analyte identification process, and was particularly useful in instances of component peak overlap, and for the identification of pyrazine analytes (e.g. 44, 88, 122 u). Semi-quantitative analysis was restricted to the 44 selcted components; however, the omission of peaks with S/N < 100, limiting the processed peaks to 1000, reduced the semi-quantitative application of the GC x GC-TOFMS method developed. Finally, results gained from GC x GC-TOFMS and GC x GC-qMS analyses were comparable with respect to spectral similarity assignments for the 44 target analytes.
Coffee↗
Molecular interconversion behaviour in comprehensive two-dimensional gas chromatography.
Comprehensive two-dimensional gas chromatography (GC x GC) is shown to provide information on dynamic molecular behaviour (interconversion), with the interconversion process occurring on both columns in the coupled-column experiment. The experiment requires suitable adjustment of both experimental conditions and relative dimensions of each of the columns. In this case, a longer column than normally employed in GC x GC allows sufficient retention duration on the second column, which permits the typical plateau-shape recognised for the interconversion process to be observed. The extent of interconversion depends on prevailing temperature, retention time, and the phase type. Polyethylene glycol-based phases were found to result in high interconversion kinetics, although terephthalic acid-terminated polyethylene glycol had a lesser extent of interconversion. Much less interconversion was seen for phenyl-methylpolysiloxane and cyclodextrin phases. This suggests that for the oximes, interconversion largely occurs in the stationary phase. Examples of different extents of interconversion in both dimensions are shown, including peak coalescence on the first column with little interconversion on the second column.
Chromatography, Gas↗
Comprehensive two-dimensional gas chromatography.
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Journal Article↗
Quantitative changes in phenolic content during physiological development of the olive (Olea europaea) cultivar Hardy's Mammoth.
This investigation was designed to characterize phenolic metabolism of the olive cultivar, Hardy's Mammoth, by examining its constitutive tissues. The phenolic profiles of pulp, seed, stone, and new and old season leaves were monitored over two fruiting seasons, to investigate possible relationships between tissues and phenol content and to determine the impact of alternate fruit bearing. No major qualitative differences in phenolic composition were found between the various tissues; however, distinct differences between the tissues with respect to quantifiable phenols were established. Relationships between 2-(3,4-dihydroxyphenyl)ethyl (3E,4E)-4-formyl-3-(2-oxoethyl)hex-4-enoate ester, oleuropein, and hydroxytyrosol in pulp and leaf were identified and found to be related to alternate bearing. Concentrations of 5-caffeoylquinic acid in old season leaves differed dramatically between seasons, confirming earlier studies.
Chromatography, High Pressure Liquid↗
Identification of phenolic compounds in tissues of the novel olive cultivar hardy's mammoth.
A methodological approach to phenolic profiling making extensive use of LC-MS with extracted ion chromatograms was applied to extracts of five different olive tissues: pulp, seed, stone, new-season leaves, and old-season leaves. Tissue extracts of the cultivars Hardy's Mammoth, Corregiola, Verdale, and Manzanillo were analyzed by HPLC with UV and ESI MS detection. Chromatograms of samples of green Hardy's Mammoth drupes, a uniquely Australian olive cultivar, were dominated by a large, broad peak. This peak was not attributable to oleuropein, which is usually the dominant phenolic compound in green olive fruit, but the phenolic compound I. This compound was isolated by semipreparative HPLC and characterized by 1D- and 2D-NMR. Extraction studies showed that the compound was not likely to be an artifact of an enzymatic degradation process. Tritium labeling studies were used to establish a possible relationship between the biosynthesis of I and oleuropein.
Chromatography, High Pressure Liquid↗