GC Stands For Greater Control

Smaller instruments, faster analyses and smarter software will extend gas chromatography's role.

By Brian G. Rohrback, Infometrix, Inc.

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Figure 5 shows an automated interpretation, via Pirouette software, of detailed hydrocarbon analysis (DHA) of winter-grade gasoline, to see if it falls within the acceptable envelope for release. The DHA table generates a matrix separating hydrocarbons both by carbon number and compound type. A chemometric analysis maps a point that scores every run and compares it to a library. Here, a single point represents each chromatogram; points close to one another are relatively similar. This approach allows us to create a confidence limit around, in this case, "good winter-grade gasoline" and instantly detect if a sample is out-of-specification.

As NeSSI-inspired sampling systems become more common, the attention is shifting toward building hardware and software that better suits the innovations in sample handling. The hardware is getting smaller, faster and easier to configure to handle an application's specific requirements. With alignment in place, it's practical to compare chromatograms from any instrument as long as they're running substantially the same method and use similar columns and conditions. Even historical data can be retrieved and brought into alignment with a more modern gold standard. Using the exact same chemometric approach we use in optical spectroscopy, we can build robust, fully automated interpretation systems to give us the final link to bringing GC truly into the control loop.

BRIAN G. ROHRBACK is president of Infometrix, Inc., Bothell WA. E-mail him at brian_rorhback@infometrix.com.

1.    Dye, T., "Update of NeSSI Market Status and SMART Module (SAM)," CPAC, Univ. of Washington, Seattle (May, 2010), http://depts.washington.edu/cpac/Activities/Meetings/Spring/2010/agenda.html
2.    Gunnell, J., "History and Overview of NeSSI," CPAC, Univ. of Washington, Seattle (November, 2008), http://depts.washington.edu/cpac/Activities/Meetings/Fall/2008/agenda.html
3.    Chrisensen, J. H., Tomasi, G. and Hansen A.B., "Chemical Fingerprinting of Petroleum Biomarkers using Time Warping and PCA," Environ. Sci. Technol., 39, p. 255 (2005).
4.    Dubois, R. N., van Vuuren, P. and Gunnell, J. J., "NeSSI (New Sampling/Sensor Initiative) Generation II Specification," CPAC, Univ. of Washington, Seattle (2003).
5.    Dubois, R. N., Novak, D. and van Vuuren, P., "Process Analytics: are there dinosaurs among us?", CPAC, Univ. of Washington, Seattle (November, 2010), http://depts.washington.edu/cpac/Activities/Meetings/Fall/2010/documents/DuboisetalCPACdinosaursNov2b2010.pdf
6.    "New Sampling/Sensor Initiative," http://cpac.apl.washington.edu/story/NeSSI%E2%84%A2
7.    "Process Analytical Systems: A Vision For The Future," http://depts.washington.edu/cpac/NeSSI/2_IFPAC_2000/VisionPaper_IFPAC2000.doc
8.    Rechsteiner, C. A., Jr., Ramos, L. S., Rohrback, B. G. and Crandall, J. A., "Towards a More Robust Process GC," Proceedings of the Instrument Society of America — 53rd Analysis Division Symposium, Session 4, Paper 2, ISA, Research Triangle Park, NC (April 2008).

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  • [Editor's Note: We are posting this comment with permission from Marcus Trygstad]

    Dr. Rohrback's review of the state of the art as it has developed in practical online gas chromatography (GC) serves to illustrate the possibility of "teaching old dogs new tricks."

    GC was the first analytical technology with a multivariable output to become broadly installed in the petrochemical industry. Four decades later, in terms of numbers installed, it remains unchallenged as top dog.

    But while techniques and technologies have improved since then, three developments signal what are arguably the first real changes to the process GC paradigm, excluding the advent of capillary columns: sampling technology (NeSSI); resistively heated capillary columns to replace the column oven (Falcon Analytical); and software that performs DHA and chemometric alignment of chromatograms (InfoMetrix Software).

    Such software transforms GC from being a largely univariate enterprise to a multivariate one, permitting reliable exploitation of the rich content from chromatograms.

    Seeing these developments, Jimmy Converse of Monsanto might rejoin Rohrback and say that GC stands for "Get creative!" In 1983, he questioned, "Why are we still using the same sample preparation techniques that we used 40 years ago?"

    He also anticipated that "We will find a way…to improve reliability and reduce cost!"

    Twenty years later, NeSSI began validating Converse's optimism, while industry's embrace today of new paradigm process GC technology suggests that NeSSI technology is enabling progress by remaking the sampling enterprise.

    Marcus Trygstad



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