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CHEMICAL FORENSIC EVIDENCE IN FIRE/EXPLOSION CAUSATION ANALYSIS - paper presented at the 2018 International Symposium on Fire Investigation Science and Technology (pdf format)
Some of the types of analytical testing which we employ are briefly described below. A detailed description of the instrumentation and methodology is provided in pdf format by clicking on the following links.
Gas chromatography separates compounds and them mass spectroscopy determines each compound's molecular mass and ionic fragments. This is a specific test that can positively identify the actual presence of a particular compound in a given sample.
Ion chromatography is an analytical technique used for the separation and determination of ions such as fluoride, chloride, nitrate, phosphate, etc., in liquids.
Infrared spectroscopy measures the wavelength and intensity of the absorption of near-infrared light by a sample. Fourier transform analysis is used to plot a spectrum relating light absorbance or transmittance and frequency (or wavelength). FTIR may be used to identify an unknown material, the consistency of a product, or the amount of components in a mixture.
MALDI-TOF is a very sensitive technique used to determine the mass of polymera, proteins, or peptides. A prepared sample mixture is irradiated with a laser, vaporizing the sample mixture into various compound fragments. The pattern of fragments is analyzed to deduce the structure of the original molecule.
SIMMS is a technique used to analyze the composition of a solid surface using ion beams. A focused ion beam is directed onto the surface of a sample resulting in particles being emitted as ions, called secondary ions. These are collected and analyzed by a mass spectrometer which produces a spectrum from which the chemical structure and elemental composition of the molecular layer (uppermost molecular layer) of a solid can be determined, including the nature and properties of adsorbed areas. SIMMS is an excellent method for mapping a surface and can provide a surface map of atoms and molecules of both organic and inorganic species of a sample.
Scanning Electron Microscopy emits a finely-focused beam of electrons onto a sample to provide a high-resolution, high-magnification image, and it can be used to analyze electron energies to create a three-dimensional image. X-rays are also produced and analyzed by an energy-dispersive x-ray instrument to produce a spectrum of peaks corresponding to energy levels. This simultaneously examines the morphology and elemental composition of samples.
Thermogravimetric analysis measures the change in weight that occurs in response to a variety of data including endotherms, exotherms, measurements of the oxidation process, thermal stability, decomposition points of explosives, characteristics of polymers, and degradation temperatures of a material.
Py-GC/MS uses high temperatures in an inert atmosphere or under vacuum to heat and degrade a sample to produce smaller and more analytically useful fragments. These fragments can be separated on a gas chromatography column and detected in a mass spectrometry instrument. A chromatogram of peaks is produced where each peak represents a compound and its relative abundance.
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