Forensic Application of Gas Chromatography)Differential Mobility Spectrometry with Two-Way Classification of Ignitable Liquids from Fire Debris Yao Lu and Peter B. Harrington* Clippinger Laboratories, Center for Intelligent Chemical Instrumentation, Department of Chemistry and Biochemistry, OHIO University, Athens, Ohio 45701-2979 With respect to the emerging role of forensic science for arson investigation, a low cost and promising onsite detection method for ignitable liquids is desirable. Gas chromatography-differential mobility spectrometry (GC- DMS) was investigated as a tool for analysis of ignitable liquids from fire debris. Headspace solid-phase microex- traction (SPME) was applied as the preconcentration and sampling method. The combined information afforded by gas chromatography and differential mobility spectrometry provided unique two-way patterns for each sample of ignitable liquid. Two-way GC-DMS data were classified into one of seven ignitable liquids using a fuzzy rule- building expert system (FuRES). The performance of the classifier was validated using bootstrap Latin partitions (BLPs) and also compared to optimized partial least- squares (PLS) classifiers. Better prediction results can be obtained by using two-way GC-DMS data than only using one-way total ion chromatograms or integrated differential mobility spectra. FuRES models constructed with the neat ignitable liquids identified the spiked samples from simulated fire debris with 99.07 ( 0.04% accuracy. Arson is the leading cause of fires and the second leading cause of deaths and injuries according to the statistics from the U. S. Fire Administration, 1 which results in lost lives and property. As a result, arson investigation is of forensic significance for the federal government, the fire service, and the criminal justice system. A variety of ignitable liquids may be used as accelerants by criminals to start a fire. Ignitable liquids are typically com- mercially available fuels or solvents that are mixtures consisting of hundreds of components. Identification is difficult because ignitable liquids may comprise the same or similar components but with different distributions of concentration. Identification is further complicated by combustion because volatile components may have evaporated from the liquid and additional pyrolysis products may be produced that can alter the composition of the residual ignitable liquids detected in fire debris. Gas chromatography/mass spectrometry (GC/MS) has proven to be an effective method for the characterization of ignitable liquids from suspected arson scenes. 2-4 GC/MS is applied as the standard American Society for Testing and Materials (ASTM) method for ignitable liquid analysis. 5 A large database of GC/MS data of ignitable liquids is available on the Internet. 6 In addition to GC/MS, a variety of methods have also been explored for ignitable liquids analysis to improve the resolution, such as heartcut multidimensional gas chromatography, 7 tandem mass spectrometry (GC/MS/MS), 8 Fourier transform ion cyclotron resonance (FTICR) high-resolution mass spectrometry, 9 and two- dimensional gas chromatography (GC × GC). 10 Although the modern analytical technology would provide the specificity needed for analyses or measurements of complex mixtures of hydrocarbon compounds, cost and maintenance have to be considered. Differential mobility spectrometry (DMS) was accomplished with a Sionex microfabricated analyzer that characterizes analytes based on the difference between ion mobilities under high and low electric fields at ambient pressure. Detailed descriptions on DMS can be found elsewhere but will be briefly explained. 11-13 The principle of separating ions by their change in mobility at different electric field strengths was proposed in 1993. 14 This technique has also been referred to as field asymmetric ion * Corresponding author. Phone: +1 740 994 0265. Fax: +1 740 593 0148. E-mail: Peter.Harrington@OHIO.edu (P. B. Harrington). (1) U.S. Fire Administration In Arson in the United States; Topical Fire Research Series; U.S. Fire Administration: Emmitsburg, MD, 2001; Vol. 1(8), pp 1-3. (2) Keto, R. O.; Wineman, P. L. Anal. Chem. 1991, 63, 1964-1971. (3) Tan, B. J.; Hardy, J. K.; Snavely, R. E. Anal. Chim. Acta 2000, 422, 37-46. (4) Wallace, J. R. J. Forensic Sci. 1999, 44, 996-1012. (5) American Society for Testing and Materials International E1618-01 Standard Test Method for Ignitable Liquid Residues in Extracts from Fire Debris Samples by Gas Chromatography-Mass Spectrometry; Document No. ASTM E 1618- 01, ASTM: West Conshohocken, PA, 2002. (6) National Center for Forensic Science website. http://www.ncfs.ucf.edu (accessed in June 2006). (7) Jayatilaka, A.; Poole, C. F. Chromatographia 1994, 39, 200-209. (8) Jayne, B.; Froneman, M.; Rohwer, E.; Sutherland, D. A. J. Forensic Sci. 2002, 47, 736-756. (9) Rodgers, R. P.; Blumer, E. N.; Freitas, M. A.; Marshall, A. G. J. Forensic Sci. 2001, 46, 268-279. (10) Frysinger, G. S.; Gaines, R. B. J. Forensic Sci. 2002, 47, 471-482. (11) Miller, R. A.; Nazarov, E. G.; Eiceman, G. A.; King, A. T. Sens. Actuators, A 2001, 91, 301-312. (12) Krylov, E.; Nazarov, E. G.; Miller, R. A.; Tadjikov, B.; Eiceman, G. A. J. Phys. Chem. A 2002, 106, 5437-5444. (13) Spangler, G. E.; Miller, R. A. Int. J. Mass Spectrom. 2002, 214, 95-104. (14) Buryakov, I. A.; Krylov, E. V.; Nazarov, E. G.; Rasulev, U. K. Int. J. Mass Spectrom. Ion Processes 1993, 128, 143-148. Anal. Chem. 2007, 79, 6752-6759 6752 Analytical Chemistry, Vol. 79, No. 17, September 1, 2007 10.1021/ac0707028 CCC: $37.00 © 2007 American Chemical Society Published on Web 08/08/2007