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Forensic Science Links

Explosives Analysis Research

Research previously done at Oak Ridge National Laboratory focused on the development of new analytical methods for the analysis of organic explosives. The extremely low vapor pressures of many organic explosives complicate the collection and analysis of these materials from the vapor phase. An analytical method developed in our laboratory facilitates the analysis of vapor phase organic explosives by means of sample introduction through thermal desorption. The method uses the injection port of a gas chromatograph as a thermal desorption unit. A vapor sampling tube is inserted directly into the injection port for desorption and the explosives are focused on the head of the analytical column at room temperature. Subsequent analysis by GC-MS with negative ion chemical ionization results in a well- resolved chromatograph (shown below right). This method has also been used in collaboration with scientists at the University of Montana to assist in the detection of explosives in honeybee hives as a way of detecting landmines.

In addition to methods development, we have reported method limits of detection for GC-MS analysis of organic explosives in electron impact (EI), positive ion chemical ionization (PICI)and negative ion chemical ionization (NICI) modes. Although the limits of detection are higher for ionization by PICI, this softer mode of ionization allows the differentiation between nitroesters based on fragmentation patterns. This differentiation is generally not achieved in EI or NICI ionization modes.

Analytes Include:
Nitroglycerine (NG)
Dinitrobenzene (DNB)
Dinitrotoluenes (DNT)
Trinitrotoluene (TNT)
Trinitrobenzene (TNB)
PETN
RDX
Aminodinitrotoluenes (x-A-y,z-DNT)
Dinitronaphthlene (DNN)
Explosives GC-MS Total Ion Chromatogram

Our current interests continue to be in the area of new analytical methods development and the identification of matrix effects on the recovery and analysis of explosives residue from post blast debris. The examination of impurity components in explosives samples as a method of identifying possible sources of a sample is also a research focus. In addition to GC-MS, LC-MS and LC-MS/MS methods are utilized to analyze inorganic oxidizers and organic explosives for forensic applications.

For more information on this research, please consult the following publications:

Sigman, M. E.; Ma, C.-Y. "In-Injection Port Thermal Desorption For the Analysis of Trace Explosives Evidence," Anal. Chem., 1999, 71, 4119.

Sigman, M. E.; Ma, C.-Y. "Operational Guideline: Teflon Dry Surface Wipe Collection and In-Injection Port Thermal Desorption Analysis of Trace Levels of Organic Explosives," ORNL/TM-1999/315.

Sigman, M. E.; Ma, C.-Y. "Detection limits for GC/MS Analysis of Organic Explosives," J. Forensic Sci. 2001, 46, 6-11.

Sigman, M. E.; Ma, C. Y.; Ilgner, R. H. "Performance Evaluation of an In-Injection Port Thermal Desorption/Gas Chromatographic/Negative Ion Chemical Ionization Mass Spectrometric Method for Trace Explosive Vapor Analysis," Anal. Chem. 2001, 73(4), 792.

Gapeev, A., Sigman, M. and Yinon, J. “Liquid Chromatography/Mass Spectrometric Analysis of Explosives: RDX Adduct Ions,” Rapid Comm Mass Spectrom., 2003, 17, 943-948.

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Ignitable Liquids Research

Our research in the area of ignitable liquids is currently focused on the analysis of vapor retention properties of commercial containers that are typically used for arson evidence collection. Our vapor retention studies are essentially long-term holding-time studies that utilize GC-MS analysis of headspace samples. Additionally, we are interested in the fundamental dynamic behavior of mixtures of hydrocarbon vapors under typical sampling conditions that are encountered when examining evidence in potential arson cases. The dynamic studies involve characterization of the behavior and distribution of hydorcarbon vapors within a closed system, as revealed through ASTM-based sampling methodologies. The distribution of hydrocarbon vapors under the sampling condition, hydrocarbon loadings and adsorption behavior can have significant influence on the hydrocarbon profile and data interpretation. These highly applied studies are in direct response to requests from the forensic science community.

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Fiber Dyes Research

The forensic analysis of fiber trace evidence usually involves a series of microscopic analyses using comparison microscopes, polarized light microscopes, microspectorphotometers (for UV-visible absorption spectral measurement), and fiber compositional analysis by FTIR-microscope. Further analysis of the dye components typically involves dye extraction followed by thin-layer chromatography or HPLC analysis with UV-visible absorption detection. Methods that rely upon UV-visible absorption spectroscopy often can not distinguish between fiber dyes differeing by a single auxochrome. Dyes that are indistinguishable by UV-visible absorption spectroscopy, are often readily diferentiated by LC-MS analysis as shown by the mass spectra in the following figure. The two dyes, acid green 25 and acid green 27 have indistinguishable absorpion profiles in the visible spectral region.

For more information on this research, please consult the following publications:

M. Huang, J. Yinon and M. E. Sigman, 2004. Forensic Identification of Dyes Extracted from Textile Fibers by Liquid Chromatography Mass Spectrometry (LC-MS). J. Forensic Sci., 2004, 49 (2), in press.

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Sampling Materials Research

Our research in sampling materials focuses on the development of functional sampling devices based on molecular imprinted polymers (MIPS). This research has only recently gotten underway. Check back soon for updates on the exciting results from this research.

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