Second-order chemometric standardization for high-speed hyphenated gas chromatography: Analysis of GC/MS and comprehensive GC�GC data

Abstract

Second-order data such as those provided by hyphenated instruments like gas chromatography with mass spectrometry detection (GC/MS) provide a wealth of information. Multichannel detection combined with multivariate analysis allows compounds that have been incompletely resolved by chromatography to be accurately quantitated. Because of this ability, chromatographic instruments can be operated in a significantly faster, reduced resolution mode. One reason this practice has not become common is that retention time variations complicate comparison of multiple data sets. In this article, an objective retention time standardization technique is presented that substantially improves quantitation. This work demonstrates a key advantage of second-order chemical analysis—that is, the ability to correct for retention time variation found in data from GC/MS analyzers and a relatively new hyphenated gas chromatographic analyzer known as high-speed comprehensive two-dimensional gas chromatography (comprehensive GC×GC). Second-order chromatographic standardization is demonstrated for the GC/MS analysis of methyltert-butyl ether (MTBE) in gasoline. The selectivity of capillary gas chromatography and mass spectrometry, combined with second-order analysis, allows this analysis to be performed in 40 s. Generalized rank annihilation method (GRAM) is used to quantify MTBE. Without standardization, an average retention time variation of 1.3% between standards and samples led to a quantitative precision error of about 20%. Second-order chromatographic standardization reduced this error to <5%. The standardization technique was also tested on comprehensive GC×GC data. In comprehensive GC×GC, the second of two columns repeatedly performed subsecond separations on portions of the effluent from a first column of different chemical selectivity. Comprehensive GC×GC of a white gas mixture modified with several test aromatic compounds was performed. The standardization demonstrated that retention times in comprehensive GC×GC are very repeatable in short column runs. GRAM was used to quantify overlapped ethylbenzene and p-xylene peaks in comprehensive GC×GC data. Because GRAM can be successfully applied to comprehensive GC×GC data, full resolution of all the analytes of interest is not necessary. As a result, comprehensive GC×GC run times can be dramatically shortened, which has significant implications for analyses in which short cycle times are of paramount importance. ©1999 John Wiley & Sons, Inc. J Micro Sep 11: 97–107, 1999