Johnson, Prazen, Young, Synovec J. Sep. Sci. 2004, 27, 410 – 416 www.jss-journal.de i 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Kevin J. Johnson 1 Bryan J. Prazen 1 Donald C. Young 2 Robert E. Synovec 1 1 Center for Process Analytical Chemistry, Department of Chemistry, Box 351700, University of Washington, Seattle, WA 98195, USA 2 Chevron Research and Technology Co., 100 Chevron Way, Richmond, CA 94802, USA Quantification of naphthalenes in jet fuel with GC6GC/Tri-PLS and windowed rank minimization retention time alignment Comprehensive, two-dimensional gas chromatography (GC6GC) is used in conjunc- tion with trilinear partial least squares (Tri-PLS) to quantify the percent weight of naphthalenes (two-ring aromatic compounds) in jet fuel samples. The increased peak capacity and selectivity of GC6GC makes the technique attractive for the rapid, and possibly less tedious analysis of jet fuel. The analysis of complex mixtures by GC6GC is further enhanced through the use of chemometric techniques, including those designed for use on 2-D data such as Tri-PLS. Unfortunately, retention time variation, unless corrected, can be an impediment to chemometric analysis. Previous work has demonstrated that the effects of retention time variation can be mitigated in sub-regions of GC6GC chromatograms through the application of an objective reten- tion time alignment algorithm based on rank minimization. Building upon this previous work, it is demonstrated here that the effects of retention time variation can be mitigat- ed throughout an entire GC6GC chromatogram with an objective retention time alignment algorithm based on windowed rank minimization alignment. A significant decrease in calibration error is observed when the algorithm is applied to chromato- grams prior to construction of Tri-PLS models. Fourteen jet fuel samples with known weight percentages of naphthalenes (ASTM D1840) were obtained. Each sample was subjected to five replicate five-minute GC6GC separations over a period of two days. A subset of nine samples spanning the range of weight percentages of naphthalenes was chosen as a calibration set and Tri-PLS calibration models were subsequently developed in order to predict the naph- thalene content of the samples from the GC6GC chromatograms of the remaining five samples. Calibration models constructed from GC6GC chromatograms that were retention time corrected are shown to exhibit a root mean square error of predic- tion of roughly half that of calibration models constructed from uncorrected chromato- grams. The error of prediction is lowered further to a value that nearly matches the uncertainty in the standard percent weight values (ca. 1% of the median percent volume value) when the aligned chromatograms are truncated to include only regions of the chromatogram populated by naphthalenes and compounds of similar polarity and boiling point. Key Words: GC6GC; Chemometrics; Jet fuel; Retention time alignment; Received: July 17, 2003; revised: October 9, 2003; accepted: October 10, 2003 DOI 10.1002/jssc.200301640 1 Introduction Comprehensive two-dimensional gas chromatography (GC6GC) is a relatively new separation technique intro- duced by Phillips and co-workers in 1991 [1]. In GC6GC, components of a mixture are subjected to analytical sep- aration on two columns with different stationary phases of complementary selectivity [2, 3]. The columns are con- nected serially, with the separation on the first column being two magnitudes of order or more longer in duration than that on the second column. Analyte molecules are transferred from the first column to the second by means of a modulating interface that provides periodic injections of first column eluent onto the head of the second column. Both thermal and valve-based modulators have been reported [4 – 6]. The resulting chromatogram is 2-D and each analyte peak has a retention time for both the first and second column separations. In addition to the increase in selectivity provided by two retention times per peak, a GC6GC instrument with properly chosen col- Correspondence: Robert E. Synovec, Center for Process Ana- lytical Chemistry, Department of Chemistry, Box 351700, Univer- sity of Washington, Seattle, WA 98195, USA. Phone: +1 206 685 2328. Fax: +1 206 685 8665. E-mail: synovec@chem.washington.edu. 410