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the samples and with multiple analysts is quite remarkable and indicates that sample complexity does not limit this method in its ability to identify compounds. Certainly, it is the combination of technologies that enable the methodology to be so successful. The accurate mass, high resolution data enables formula identification while the database similarity and retention index search combine to verify the known unknowns. In particular, the GCxGC technology expands the chromatographically available space significantly, improving chromatographic resolution which leads to dramatically improved peak detection compared to traditional, single dimension chromatography.
Conclusions
We have addressed several of the goals of the study. By identifying up to 90% of the spiked standards we believe that this method and processing performs exceedingly well and the complexity of the mixture did not impact the performance of identifications. However, we have not yet evaluated the unintended components which likely resulted in these mixtures.
Many aspects of interpretation continue to be investigated and this will be done in future work. For example, performing the same GCxGC experiments on the neat standards of each analyte (almost 4000 injections!) to take our confidence of the identification to the highest level. We are very optimistic of the accuracy of identifications once that work is complete.
Acknowledgements
The authors would like to thank Drs. Elin Ulrich and Jon Sobus (US EPA) for their efforts in initiating and coordinating this trial. Dr. Elizabeth Humston-Fulmer, Dr. David Alonso and Christina Kelly (LECO- US) provided significant assistance in data acquisition, methodology development, data review, and analysis.
References
1. Sobus, J. R., et al. (2017). “Integrating tools for non-targeted analysis research and chemical safety evaluations at the US EPA.” Journal of Exposure Science & Environmental Epidemiology.
2. Schymanski, Emma L., et al., “Identifying small molecules via high resolution mass spectrometry: communicating confidence”, Environ Sci Technol. 2014;48:2097-2098.
3. Schymanski, Emma L., et al., Non-Target Screening high high-resolution mass spectrometry: critical review using a collaborative trial on water analysis”, Anal Bioanal Chem 2015, 407:6237-6255
4. “The History of the NIST/EPA/NlH Mass Spectral Database”, Today’s Chemist at Work February 1999 Today’s Chemist at Work, 1999, 8(2), 45-46, 49-50.
5.
http://www.americanlaboratory. com/913-Technical-Articles/340911- Introduction-of-NIST-17-A-Major-Update- of-Mass-Spectral-Libraries-and-Software- at-the-65th-ASMS-Conference-on-Mass- Spectrometry-and-Allied-Topics/
6. Wallace, William E., et al. “Mass spectral library quality assurance by inter-library comparison.” Journal of The American Society for Mass Spectrometry 28.4 (2017): 733-738.
7. Ausloos, P., et al. “The critical evaluation of a comprehensive mass spectral library.” Journal of the American Society for Mass Spectrometry 10.4 (1999): 287-299.
8.
https://www.nist.gov/srd/nist-standard- reference-database-1a-v17
9. Sumner, Lloyd W., et al. “Proposed minimum reporting standards for chemical analysis working group (CAWG) Metabolomics Standards Iniative (MSI)” Metabolomics, 2007, 3(3), 211-221
10.EPA CompTox Chemistry Dashboard
https://comptox.epa.gov/dashboard
11.McLafferty, Fred W., Turecek, Franstisek, Interpetation of Mass Spectra, 4th edition, 1993
12.Matthew S. Klee, Jack Cochran, Mark Merrick, Leonid M. Blumberg, Evaluation of conditions of comprehensive two- dimensional gas chromatography that yield a near-theoretical maximum in peak capacity gain, Journal of Chromatography A, Volume 1383, 2015, Pages 151-159
13.Lee, Andrew L., A Model of Peak Amplitude Enhancement in Orthogonal Two-Dimension Gas Chromatography, anal. Chem., 2001, 73, 1330-1335
14.Simply GCxGC. Free online tool for understanding method optimization of GCxGC
www.leco.com/simply-gcxgc
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