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Table 2 GCxGC-QTOFMS Instrument Conditions - Essential Oil Parameter


Setting


GC Conditions Primary Column


Secondary Column Split Ratio


Split Inlet Temperature


Oven Temperature Program Carrier Gas Flow


Modulation Conditions Modulator


Modulation Period Cold Jet Flow


Hot Jet Temperature MS Conditions


Transfer Line Temperature Ionisation Mode


Data Acquisition Rate


280°C EI


50 Hz


One-Sample Class Example: Essential Oils


The second example analysed data of 10 essential oils including Cardamom, Clove Bud, Coriander, Fennel, Ginger Oil, Juniper Berry, Lavender, Nutmeg, Peppermint, and Turpentine [13]. Only one sample was collected for each type of essential oil. The 10 samples were analysed using the GCxGC- QTOFMS system with Agilent 7890A GC/ Zoex ZX2 thermal modulation system coupled with Agilent 7200 Q-TOF. Samples were directly injected. The instrument conditions are summarised in Table 2.


The Investigator framework extracted 35 reliable peaks used for alignment and 1352 peak-regions used to create a feature template. The following criteria were used to search:


• Detection Filter: SNR > 10,


• Cross-Sample Significance Check: Relative SNR Threshold = 0.1,


Conclusion Classical statistical tools are useful but


• Cross-Sample Identification Check: Spectral Match Factor Threshold = 500.


There are 12 common features and 319 unique features found from total 1352 features as shown in Figure 5. On the left, the composite chromatogram is overlaid with all extracted features indicated by purple rectangles. On the right, a bubble plot shows common and unique features with average percent response as bubble sizes and class labels determined by the above criteria. Figure 6 shows one of the distinctive features for Lavender. In the chromatogram of Juniper Berry, this feature peak-region is a background region; and, in the chromatogram of Ginger Oil, it contains another compound with a different spectrum. Without the cross-sample identity check, this feature would not be found as a unique compound for Lavender.


DB-1, 30 m × 0.25 mm × 0.25 µm DB-17, 1.5 m × 0.1 mm × 0.1 µm 10:1


265°C


45°C to 280°C at 2.2°C/min 1 mL/min


Zoex ZX2


4.5 seconds 18 L/min


170°C to 375°C at 2.5°C/min


not sufficient for real-world cross-sample data analysis. The new workflow and associated tools described above combine classical statistical tools with advanced data processing, filtering, and visualisation in order to detect common and unique compounds across multiple samples. The workflow was demonstrated with two typical untargeted analysis cases with GCxGC- QTOFMS data. The same workflow can be used to analyse multiple classes of samples with any comprehensive two-dimensional chromatography technique.


References


1. Alonso, Arnald, Sara Marsal, and Antonio Julià. “Analytical Methods in Untargeted Metabolomics: State of the Art in 2015.” Frontiers in Bioengineering and Biotechnology 3 : 23. 2015.


2. Tranchida, P. Q., Franchina, F. A., Dugo, P. and Mondello, L. “Comprehensive two-dimensional gas chromatography- mass spectrometry: Recent evolution and current trends.” Mass Spec Rev, 35: 524–534. 2016.


3. Isabelle François, Koen Sandra, Pat Sandra, “Comprehensive liquid chromatography: Fundamental aspects and practical considerations—A review”, In Analytica Chimica Acta, Volume 641, Issues 1–2, Pages 14-31, 2009.


4. S. Reichenbach, X. Tian, Q. Tao, E. Ledford, Z. Wu, O. Fiehn. “Informatics for Cross-Sample Analysis with Comprehensive Two-Dimensional Gas Chromatography and High-Resolution Mass Spectrometry (GCxGC-HRMS).” Talanta, 83(4):1279-1288, 2011.


5. S. Reichenbach, X. Tian, C. Cordero, Q. Tao. “Features for non-targeted cross- sample analysis with comprehensive two- dimensional chromatography.” Journal of Chromatography A, 1226:140-148, 2012.


Figure 5. Untargeted Analysis of 10 Essential Oils. The new workflow is able to find potential common and unique compound features (right) from all features of all samples (left).


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