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.
USING A GC FOR CONTROL
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 email@example.com.
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