Adaptive Two-Dimensional Microgas Chromatography Jing Liu, †,‡ Maung Kyaw Khaing Oo, †,‡ Karthik Reddy, †,‡,§ Yogesh B. Gianchandani, ‡,§ Jack C. Schultz, ⊥ Heidi M. Appel, ⊥ and Xudong Fan* ,†,‡ † Department of Biomedical Engineering, University of Michigan, 1101 Beal Avenue, Ann Arbor, Michigan 48109, United States ‡ Center for Wireless Integrated Microsensing and Systems, University of Michigan, 1301 Beal Avenue, Ann Arbor, Michigan 48109, United States § Department of Electrical Engineering and Computer Science, University of Michigan, 1301 Beal Avenue, Ann Arbor, Michigan, 48109, United States ⊥ College of Agriculture, Food, and Natural Resources, University of Missouri, Bond Life Sciences Center, 1201 E. Rollins Road, Columbia, Missouri, 65211, United States * S Supporting Information ABSTRACT: We proposed and investigated a novel adaptive two-dimensional (2-D) microgas chromatography system, which consists of one 1st-dimensional column, multiple parallel 2nd-dimensional columns, and a decision-making module. The decision-making module, installed between the 1st- and 2nd-dimensional columns, normally comprises an on- column nondestructive vapor detector, a flow routing system, and a computer that monitors the detection signal from the detector and sends out the trigger signal to the flow routing system. During the operation, effluents from the 1st-dimen- sional column are first detected by the detector and, then, depending on the signal generated by the detector, routed to one of the 2nd-dimensional columns sequentially for further separation. As compared to conventional 2-D GC systems, the proposed adaptive GC scheme has a number of unique and advantageous features. First and foremost, the multiple parallel columns are independent of each other. Therefore, their length, stationary phase, flow rate, and temperature can be optimized for best separation and maximal versatility. In addition, the adaptive GC significantly lowers the thermal modulator modulation frequency and hence power consumption. Finally, it greatly simplifies the postdata analysis process required to reconstruct the 2-D chromatogram. In this paper, the underlying working principle and data analysis of the adaptive GC was first discussed. Then, separation of a mixture of 20 analytes with various volatilities and polarities was demonstrated using an adaptive GC system with a single 2nd-dimensional column. Finally, an adaptive GC system with dual 2nd-dimensional columns was employed, in conjunction with temperature ramping, in a practical application to separate a mixture of plant emitted volatile organic compounds with significantly shortened analysis time. M icrogas chromatography (μGC) has attracted tremen- dous research interest due to its wide applications in areas such as environmental protection, 1,2 biomedical diag- nostics, 3,4 industrial monitoring and occupational safety, 5 homeland security, and the battlefield. 6-8 As compared to the conventional benchtop GC, μGC offers a compact size, a lightweight, and the ability to conduct rapid, on-site vapor analysis. However, μGC achieves these advantages at the expense of separation capability, which is one of the most important features of a GC system in analyzing complex gas mixtures. This loss of separation capability is due primarily to the shortened length of the separation columns used. To date, a number of methods have been developed to address this challenge, 2,9-19 among which comprehensive two-dimensional GC (or 2-D GC) technology is the best and most widely used solution. This technology utilizes two GC columns connected in series and coated with different stationary phases. 12,13,15,19 A modulator is installed between the two GC columns. It collects the effluent from the 1st-dimensional column, focuses it into a very narrow band, and then reinjects it into the 2nd- dimensional column for additional separation. Since analytes undergo two independent separations, they can be differ- entiated from each other on a 2-D chromatogram by the retention time in the 1st- and the 2nd-dimensional column. Despite the significantly improved separation capability, existing 2-D GC technology faces several challenges. (1) Since the modulator has to continuously cut and send the effluent from the 1st-dimensional column to the 2nd-dimensional column at a high frequency, the separation at the 2nd- dimensional column needs to be finished within only a few seconds before the modulator injects the next effluent to the 2nd-dimensional column, which greatly limits the separation Received: February 28, 2012 Accepted: April 2, 2012 Published: April 2, 2012 Article pubs.acs.org/ac © 2012 American Chemical Society 4214 dx.doi.org/10.1021/ac300588z | Anal. Chem. 2012, 84, 4214-4220