Arson identification

Elderd, D. M. Kildahl, N. K. Berka, L. H. Experiments for Modern introductory Ghemistry identification of Arson Accelerants by Gas Ghromatography, /. Chem. Educ. 1996, 73, 675-677. 

This collector has the formula shown in Figure 21.3. The identification of /7-tolyl arsonic acid as a selective collector for cassiterite flotation led to the introduction of this collector into many industrial plants. The first recorded industrial use of /7-tolyl arsonic acid was at the Alterberg mine in Germany. By the early 1970s, this collector was introduced into a number of operations, including Rooiberg and Union Tin (South Africa), the Renison and Cleveland tin mines (Australia). 

Cell Culture As Mass spectrometry Identification of arsenate, arsenite, monomethyl-arsonate and dimethyl-arsinate 89)... 

HPLC units have been interfaced with a wide range of detection techniques (e.g. spectrophotometry, fluorimetry, refractive index measurement, voltammetry and conductance) but most of them only provide elution rate information. As with other forms of chromatography, for component identification, the retention parameters have to be compared with the behaviour of known chemical species. For organo-metallic species element-specific detectors (such as spectrometers which measure atomic absorption, atomic emission and atomic fluorescence) have proved quite useful. The state-of-the-art HPLC detection system is an inductively coupled plasma/MS unit. HPLC applications (in speciation studies) include determination of metal alkyls and aryls in oils, separation of soluble species of higher molecular weight, and separation of As111, Asv, mono-, di- and trimethyl arsonic acids. There are also procedures for separating mixtures of oxyanions of N, S or P. 

Recovery and Identification of Residues of Flammable Liquids from Suspected Arson Debris... 

Lewisite 1 per se is never found in the environment. Figure 18 shows that this compound hydrolyzes rapidly on contact with moisture to 2-chlorovinyl arsonous acid, which in turn slowly dehydrates to lewisite oxide (syn. 2-chlorovinyl arsenous oxide) (16). Both 2-chlorovinyl arsonous acid and lewisite oxide are nonvolatile. The most frequently used method for the identification of CWC-related chemicals is based on gas chromatography (GC) in combination with mass spectrometry (GC/MS). Indirect GC/MS analysis of lewisite 1 requires sample preparation, which involves conversion of lewisite oxide to 2-chlorovinyl arsonous acid in an acidic environment, followed by derivatization (12). The obtained species is both volatile and thermally stable, and thus amenable to GC analysis. Often, a mercaptan reagent is used as a derivatization agent. The reaction with 3,4-dimercaptotoluene is shown in Figure 19. 

Gas chromatography (GC) (a) Analysis of alcohol in blood (b) Identification of possible fuels at the scene of an arson. 

Mr. Mldklff continues, "When a sample from a suspected arson is examined by gas chromatography, additional peaks from materials present at the scene, as for example, plastics, in the sample may be observed. These additional peaks make difficult pattern recognition, normally relied upon for detectlon/ldentlfIcation of flammable liquids in the debris. Similar problems may be encountered in the analysis of samples from a bomb scene where chemicals in soil or debris from the bomb crater complicate the detection and identification of explosive components. 

Following ultraviolet-visible spectrophotometry and infrared (IR) spectroscopy, gas chromatography (GC) was one of the first instrumental techniques to help in solving forensic science problems. The early very successful applications included the determination of blood alcohol by direct injection of blood or serum, and the detection and identification of petroleum products in debris from arson cases in 1958/59. The breakthrough of GC in these areas and in drug analysis was an event of the 1960s and the 1970s. 

GC was introduced very early as the technique of choice for the detection and identification of accelerants in debris from arson cases because of its high selectivity and sensitivity. But to use the full potential of the technique the methods of recovery of traces of common accelerants from fire debris had to be developed and adjusted. The used methods include solvent extraction, direct headspace analysis, and enrichment by adsorbent-based techniques. In the past, the most common concentration steps prior to the analysis have been (heated) headspace direct injection using a gastight syringe for analyte collection and GC injection or headspace adsorption techniques, mostly using charcoal followed by carbon disulfide (CSi) elution. Some of these procedures have been quite effective and are standardized by... 

See alsa Forensic Sciences Arson Residues Drug Screening in Sport Expiosives liiicit Drugs Paints, Varnishes, and Lacquers Systematic Drug Identification Voiatiie Substances. 

Debris recovered from the fire scene is often wet and burned, and may consist of material such as wood, carpet, carpet padding, tile, and other synthetic materials, all of which can contribute interfering volatile pyrolysis products that can make the identification of the accelerants difficult. The loss of accelerants through adsorption into the debris, evaporation from the heat of the blaze, and the presence of water all contribute to make the identification of accelerants a challenging task. GC can be a powerful tool in the analysis to separate and identify the accelerant in the presence of these interferences. Fultz and DeHaan have written an excellent chapter on GC in arson and explosive analysis (156). 

New methodologies and the use of selected-ion monitoring (SIM) have made GCMS the detector of choice. GCMS has been used in the past for the detection and identification of single components, such as solvents, or ignitable liquid products with few components. Forensic scientists recognized the value of the mass spectrometer for identification of compounds in arson debris as early as 1976 (197). It had not been used routinely in the crime laboratory, however, until recently. 

The forensic scientist is occasionally asked to compare brands of gasoline for the determination of common source or for the identification of the brand used in the arson. Unfortunately, brand identification is extremely difficult and, depending on the sample, it may even be impossible (155). The main reasons for this difficulty are the marketing practices of the refinery industry and the changes the product undergoes in storage. 

Keto, R. O. (1995). GC/MS data interpretation for petroleum distillate identification in contaminated arson debris, Journal of Forensic... 

---