Johnson, Prazen, Olund, Synovec 297 Kevin J. Johnson, Bryan J. Prazen, Roy K. Olund, Robert E. Synovec Center for Process Analytical Chemistry, Department of Chemistry, Box 351700, University of Washington, Seattle, Washington 918195 – 1700, USA GC6GC temperature programming requirements to produce bilinear data for chemometric analysis* A diaphragm valve-based comprehensive two-dimensional gas chromatography (GC6GC) instrument with the two columns under independent temperature control is demonstrated. A fifteen-component mixture of alkanes, alkyl aromatics, ketones, and alcohols was separated using this system in only 45 s. Independent temperature control of the two columns allows for high-speed analysis of complex samples while retaining the bilinear data structure that is necessary to apply many chemometric peak-resolving methods. An important part of high-speed GC6GC is sharp injections onto the second column. In this work, 10-ms peak widths on the second column are demonstrated. A peak capacity per time of 240 peaks/min was readily achieved. This work is aimed at providing a high-speed GC system for the quantitative and qualita- tive analysis of complex process streams, such as natural products. Key Words: Comprehensive two-dimensional gas chromatography; GC6GC; Che- mometrics; Bilinear data; Generalized rank annihilation method, GRAM; Multivariate data analysis; Received: July 7, 2001; revised: October 30, 2001; accepted: November 1, 2001 1 Introduction Due to the added degree of selectivity and increased peak capacity, chromatographic instruments containing multi- ple columns have long been valued as an important tool in the analysis of complex mixtures [1]. Comprehensive two- dimensional chromatographic separations are a form of multi-column separation in which all the chemical compo- nents in the sample are subject to two complementary separations [2 – 4]. The gas chromatographic form of this method is known as comprehensive two-dimensional gas chromatography (GC6GC). GC6GC was pioneered by J.B. Phillips in order to facilitate the analysis of compli- cated mixtures that had previously been impractical or impossible to analyze with one-dimensional GC [5]. Furthermore, GC6GC can speed up the analysis of com- plex mixtures and improve the identification of compounds through two independent retention times [6]. Over the past decade GC6GC has evolved into a very powerful gas chromatographic separation technique and a popular area of research [7 – 14]. As the instrumentation of GC6GC evolves, there are a variety of ways in which to interface the two columns. In most cases, GC6GC instruments are designed to use thermal focusing tech- niques, either heating or cooling, to produce sample injec- tions onto the second column [5 – 9, 14]. More recently, diaphragm valves are becoming a simple and rugged means to perform high-speed GC6GC [10–13]. A pri- mary difference between the two modulation methods is that thermal focusing techniques often are set up to send all of the effluent from the first column to the second col- umn. This relaxes the requirement of the number of sec- ond column separations performed on each peak eluting from the first column in order to be able to accurately quantify resolved components. In either thermal modula- tion or valve-based modulation, each injection onto the second column generates a relatively high-speed, sec- ondary chromatogram. In order to retain the resolution achieved by the first column separation and, in the case of the valve-based system, in order to maintain quantitative accuracy, a minimum number of second column separa- tions must be obtained across the width of a given peak eluting from the first column [4, 15]. To be on the safe side, one study suggests that, in order to not throw away resolution from the first column while sampling onto the second column, a minimum of four injections across the narrowest peak width eluting from the first column is necessary [15]. A more recent study demonstrated that the requirement of four injections to the second column across the narrowest first column peak is sufficient to pro- vide excellent quantitative accuracy and precision [16]. Thus, by maintaining a proper sampling frequency between the two columns, one can achieve a comprehen- sive separation with accurate, precise quantification and optimal resolution. J. Sep. Sci. 2002, 25, 297–303 Correspondence: Prof. Robert E. Synovec, Center for Pro- cess Analytical Chemistry, Department of Chemistry, Box 351700, University of Washington, Seattle, Washington 918195 – 1700, USA. E-mail: Synovec@chem.washington.edu Fax: +1 206 685 8665 * Presented at the 24 th International Symposium on Capillary Chromatography, Las Vegas, NV, USA, May 20 – 24, 2001. i WILEY-VCH Verlag GmbH, 69469 Weinheim 2002 1615-9306/2002/0504–0297$17.50+.50/0 Peer-review of papers in the section “Microcolumn Separations” was super- vised by Milton L. Lee and Pat Sandra. Their editor- ial support is gratefully acknowledged. Microcolumn Separations