The effects of microbial degradation on ignitable liquids

The identification of ignitable liquid residues in fire debris is a key finding for determining the cause and origin of a suspicious fire. However, the complex mixtures of organic compounds that comprise ignitable liquids are susceptible to microbiological attack following collection of the sample. Biodegradation can result in selective removal of many of the compounds required for identification of an ignitable liquid. Such degradation has been found to occur rapidly in substrates such as soil, rotting wood, or other organic matter. Furthermore, fire debris evidence must often be stored for extended periods at room temperature prior to analysis due to case backlogs and available evidence storage. Hence, extensive damage to ignitable liquid residues by microbes poses a significant threat to subsequent laboratory work. In this work, the effects of microbial degradation of ignitable liquids in soil have been evaluated as a function of time. Key findings include the loss of n-alkanes, particularly C₉–C₁₆, which showed the most dramatic decrease in gasoline as well as the petroleum distillates, while branched alkanes remained unchanged. Monosubstituted benzenes also showed the most dramatic loss in gasoline. In the heavy petroleum distillates, n-alkanes with even carbon numbers were degraded more than n-alkanes with odd carbon numbers. Figure A “fully involved” house fire in Indianapolis, IN

Fire debris analysis by Raman spectroscopy and chemometrics

A paper reporting the use of Raman spectroscopy in fire debris analysis is presented. Five polymer based samples, namely carpet (polypropylene), nylon stockings (nylon), foam packaging (polystyrene), CD cases (polystyrene) and DVD cases (polypropylene) were burnt with each one of the following ignitable liquids: petrol, diesel, kerosene and ethanol. Raman shifts were obtained and, in some cases, peaks were identified to correspond to pyrolysis products in the form of alkanes, aromatic or polyaromatic compounds. All pyrolysis peaks were used to produce a Principal Component Analysis (PCA) of the burned samples with the different ignitable liquids. The change in the Raman spectra made it possible to identify some of the pyrolysis products produced in the combustion and also to identify the different plastic materials in fire debris, even when different fuels have been used and the chemical and structural identity of the plastic has been altered in the fire.     

一种改进的SPME方法提取火场残留物中的促燃剂

对当前国内外用于火场残留物中促燃剂的提取方法进行研究,包括采用活性炭片法(ACS)、固相微萃取(SPME)以及对固相微萃取技术从传统的热解吸模式到溶剂脱附模式的扩展性思考。通过提取3种促燃剂(汽油,煤油和柴油)检材的效能比较与分析,优化了实验条件,确定了SPME的提取和溶剂脱附的方法,实验研究表明,SPME-溶剂脱附法是火场促燃剂残留物分析的有效方法之一。     

Determination of gasoline and diesel residues on wool,silk, polyester and cotton materials by SPME–GC–MS

The identification of ignitable liquids is very important and challenging aspect in arson crime investigations. The detection of gasoline and diesel fuel components using solid phase micro-extraction prior to gas chromatography–mass spectrometry for the forensic analysis of fire debris has been carried out. Previous works show that the absorption characteristics of the substrate are one of the most important factors in determining the evaporation rate of the accelerants. In order to determine the presence of the fuel residues, four of the most common substrate materials were tested in this work; wool, cotton, silk and polyester. The obtained results indicate that both gasoline and diesel fuel accelerants persisted longer on wool and silk than on the other selected substrates. Such information illustrates the influence of fuel persistence times after extinguishing and the best materials to be scanned for ignitable liquids at the fire scene.     

Analytical tools for the analysis of fire debris. A review: 2008–2015

The analysis of fire debris evidence might offer crucial information to a forensic investigation, when for instance, there is suspicion of the intentional use of ignitable liquids to initiate a fire. Although the evidence analysis in the laboratory is mainly conducted by a handful of well-established methodologies, during the last eight years several authors proposed noteworthy improvements on these methodologies, suggesting new interesting approaches. This review critically outlines the most up-to-date and suitable tools for the analysis and interpretation of fire debris evidence. The survey about analytical tools covers works published in the 2008–2015 period. It includes sources of consensus-classified reference samples, current standard procedures, new proposals for sample extraction and analysis, and the most novel statistical tools. In addition, this review provides relevant knowledge on the distortion effects of the ignitable liquid chemical fingerprints, which have to be considered during interpretation of results.     

Recent advances in the applications of forensic science to fire debris analysis

The forensic discipline of ignitable liquid and fire debris analysis is rapidly changing. Refinements in existing methods as well as development of new techniques are changing the routine methods of analysis. Optimization of existing extraction techniques and research into novel methods of extracting debris have improved the recovery of ignitable liquids from debris samples. The application of highly specialized instrumentation to problems of sensitivity and matrix interference has resulted in new ways of performing chemical analyses, allowing for improved limits of detection. Preliminary research in novel approaches to ignitable liquid comparisons is being evaluated, with the hopes of providing more detailed information to the field investigators. Research into a variety of areas related to fire debris analysis is ongoing, and will continue to improve the quality of ignitable liquid residue analysis.     

Extraction and concentration of vapors from fire debris for forensic purposes: Evaluation of the use of Radiello Passive Air Sampler

The Radiello Passive Air Sampler is one of the latest innovations developed for the sampling of pollutants in the air by passive headspace. It has been reported that its properties allow an enhanced sensitivity, reproducibility and adsorption capacity. It therefore appears to be of interest in the extraction of potential residues of ignitable liquids present in fire debris when arson is suspected.A theoretical approach and several laboratory tests have made it possible to precisely characterize in a forensic perspective the potential of the device in extracting and concentrating the vapors of ignitable liquids found in fire debris. Despite some advantages, the Radiello device appears to be less efficient than traditional axial symmetry samplers.     

Application of solid-phase microextraction to the recovery of explosives and ignitable liquid residues from forensic specimens

A current review of the application of solid-phase microextraction (SPME) to the analysis of ignitable liquids and explosive residues is presented along with experimental results demonstrating the relative effects of controllable variables. Variables discussed include fiber chemistry, adsorption and desorption temperatures, extraction and desorption times, fiber sampling placement (direct, headspace, and partial headspace) and matrix effects, including water content. SPME is shown to be an inexpensive, rapid and sensitive method for the analysis of ignitable liquids and high explosives residues from solid debris samples and from aqueous samples. Explosives are readily detected at parts per trillion concentrations and ignitable liquids are reproducibly detected at levels below those using conventional methods.     

火灾现场残留物中助燃剂提取及检测方法研究进展

综述了近10年来火灾现场助燃剂残留物的提取及检测方法,并对火场助燃剂残留物的检测进行了展望.     

The effects of season and soil type on microbial degradation of gasoline residues from incendiary devices

The primary task of a fire debris chemist is to determine if there is an ignitable liquid present in a fire debris sample and, if so, to classify it according to its boiling point and carbon number range. However, in organic-rich substrates such as soil, the ignitable liquid residue is subject to microbial degradation due to the ease with which bacteria can metabolize the various hydrocarbons present. This is a rapid process which is problematic in many forensic laboratories as fire debris is often stored for extended periods of time due to case backlog. Although microbial degradation has been studied in laboratory samples, it has not been well-studied in “real-world” samples, which have not only been exposed to microbial degradation but have also suffered the effects of weathering due to the intense heat of the fire. In this work, the effects of microbial degradation of gasoline from an incendiary device have been evaluated over time. In addition to visually monitoring chromatographic changes, this work also utilizes multivariate statistical techniques to simplify the complex data set and elucidate trends that might not otherwise be observed. Results indicate a clear difference between glass samples, which suffered the loss of low boiling compounds, and soil, which suffered the loss of the normal alkanes and lesser substituted aromatics. Also, devices deployed on lawn soil and in the winter season appear to show the most extensive degradation of gasoline. Finally, while the ratio of the C₃-alkylbenzenes is significantly altered in soil samples recovered from large devices, the overall chromatographic profile of gasoline recovered from smaller incendiary devices is significantly lower.

A Forensic Approach to Evaluate the Effect of Different Matrices and Extraction Solvents for the Identification of Diesel Residue in Simulated Arson by GC–MS

Chromatographia - Investigation of an arson case presents several challenges to the forensic investigator. Identification of the ignitable liquid residues in the fire debris is one of the crucial...     

A simple,inexpensive, rapid,sensitive and solventless technique for the analysis of accelerants in fire debris based on SPME

The current method of choice for the extraction of flammable or combustible liquid resides from fire debris samples is passive headspace concentration using activated charcoal strips (ACS) for adsorption of the liquid residues followed by elution with carbon disulfide or other suitable solvent. Presently, we report a new technique based on headspace solid-phase microextraction which has been successfully applied to the identification of a wide range of accelerants commonly seen in arson analysis. The SPME technique developed is simple, inexpensive, rapid, and eliminates the use of the highly flammable and toxic solvent carbon disulfide. Results using this SPME method have been directly compared to results obtained via the ACS technique for light, medium, and heavy petroleum distillates as well as gasoline. All of the accelerants studied were accurately identified by the SPME method with equal or greater sensitivity compared to the ACS method.     

火场助燃剂检验鉴定的干扰研究进展

火灾是影响公共安全最为常见的灾害之一,而放火更是严重威胁人民群众生命财产安全,属于典型的暴力犯罪.犯罪嫌疑人为了达到有效快速放火的目的,往往使用助燃剂实施放火,因而助燃剂的检验鉴定对于认定火灾性质起着至关重要的作用.然而火场情况复杂,容易对助燃剂物证检验鉴定产生较大干扰.在火灾发生发展的过程中,火场高温热环境会作用于已...     

裂解气相色谱-质谱分析火场残留物中助燃剂

通过对火灾现场助燃剂及其燃烧残留物进行分析，开展了基于裂解气相色谱-质谱法（PyGC-MS）的火场助燃剂分析方法。选取了汽油和柴油2种助燃剂以及棉布和聚对苯二甲酸乙二醇酯（PET）塑料2类载体，制备了助燃剂与载体的混合燃烧残留物。利用热分析技术确定样品的特征性温度，并对分析条件进行优化与选择。通过闪蒸分析和裂解分析的分步裂解方法，对样品进行了PyGC-MS分析。实验结果表明，PET载体原样燃烧残留物的裂解产物共有35个组分，而PET载体与汽油混合燃烧残留物和PET载体与柴油混合燃烧残留物的裂解产物只有25个组分，且各裂解产物的种类和含量均不相同。该法可对同一载体的自身燃烧残留物和与助燃剂混合燃烧残留物进行区分，适用于火灾残留物中助燃剂的分析，可对火场中是否存在助燃剂进行判别，为火灾性质的判断和火灾调查工作提供科学依据。     

新型碳基渗滤膜在易燃液体残留物提取检验中的应用

用自制的碳基渗滤膜,以自制的红外提取装置测定了该膜对苯的回收率为68%,考察了温度、压力、提取时间等对碳基渗滤膜应用的影响,主要介绍了将该碳基渗滤膜应用于现场易燃液体残留物的提取,通过水泥地面添加易燃液体的提取检验,棉布、化纤布上易燃液体残留物的提取检验测试了碳基渗透膜的提取回收能力.该碳基渗滤膜可以应用于纵火现场易燃液体残留物的提取检验.     

Analysis of Petroleum Distillates from Fire Debris Using Supercritical Fluid Extraction with a Two‐Level Orthogonal Array Experimental Design

A supercritical fluid extraction (SFE) method was developed in the present study as an effective sample pretreatment technique of petroleum distillates from fire debris. Three petroleum distillates were used as target analytes, including 95 unleaded gasoline, kerosene, and premium diesel. An orthogonal array (L16) experimental design was adopted to separately evaluate primary SFE experimental factors. The SFE efficiencies of petroleum distillates at various extraction conditions were examined and the optimized SFE conditions were identified. Experimental results demonstrated that the optimized SFE method not only provided an effective extraction method for the spiked sample, but also successfully recovered residues of petroleum distillates from fire debris.     

Headspace Single Drop Microextraction for the Analysis of Fire Accelerants in Fire Debris Samples

Fire accelerants such as gasoline, kerosene, and diesel have commonly been used in arson cases. Improved analytical methods involving the extraction of fire accelerants are necessary to increase sample yield and to reduce the number of uncertain findings. In this study, an analytical method based on headspace single drop microextraction (HS-SDME) followed by gas chromatography–flame ionization detection (GC-FID) has been developed for the analysis of simulated fire debris samples. Curtain fabric was used as the sample matrix. The optimized conditions were 2.5 μL benzyl alcohol microdrop exposed for 20 min to the headspace of a 10 mL aqueous sample containing accelerants placed in 15-mL sample vial and stirred at 1500 rpm. The extraction method was compared with the solvent extraction method using n-hexane for the determination of fire accelerants. The HS-SDME process is driven by the concentration difference of analytes between the aqueous phases containing the analyte and the organic phase constituting the microdrop of a solvent. The limit of detection of HS-SDME for kerosene was 1.5 μL. Overall, the HS-SDME coupled with GC-FID proved to be rapid, simple and sensitive and a good alternative method for the analysis of accelerants in fire debris samples.     

Chromatography–mass spectrometry identification of polyaromatic hydrocarbons in thermally modified petroleum products and thermal destruction products of organic materials of various origins

Polyaromatic hydrocarbons in samples of thermally treated petroleum products and thermal destruction products of organic materials of various origins are studied. Samples of kerosene, diesel fuel, and gasoline of different grades, that is, light flammable petroleum products often used as combustion initiators; wood; flooring (linoleum); and offset paper are selected as test samples. A pattern for determining these samples by chromatography–mass spectrometry against the background of other products formed under fire conditions is developed. It is suggested to use the limiting value of the intensity ratios of the peaks of tri- and bicyclic condensed arenes in trace residues of the combustion initiator, modified as a result of evaporation and burnup, as an identification parameter. This approach expands the range of tasks in identifying the source of environmental pollution and in determining traces of combustion initiator for forensic and fire-technical expertise.     

分析测试新成果(230~237)2种常见燃油添加剂对汽油燃烧烟尘的影响

采用气相色谱-质谱(GC-MS)联用技术,根据汽油原样中的特征成分,对未加入和分别加入汽油燃油精、海龙燃油宝的汽油燃烧烟尘进行对比分析.结果表明,汽油燃油精的加入会使汽油燃烧烟尘中各类特征成分的百分含量有所变化,但对谱图和特征成分的影响较小;而海龙燃油宝的加入对汽油燃烧烟尘的谱图、特征成分及其个数、各类特征成分的百分含量均产生较大影响.结果为火灾物证鉴定提供一定的参考依据.     

固相微萃取GC-MS快速分析火场残留物中汽油成分

火场残留物如碳灰、烧残物等通常经过样品预处理后进行分析鉴定。传统的样品预处理方法往往操作繁琐、费时、重复性差,而且需用大量有机溶剂,不利于分析人员的身体健康,对环境也会造成一定污染。固相微萃取(solid-phasemicroextraction,SPME)是在固相萃取技术的基础上发展起来的一项新的样品预处理技术,于1989年由加拿大Waterloo大学的J.Pawliszyn教授等首次提出,1993年美国的Supelco公司推出了商业化的固相微萃取设备。该技术具有快速、高效、简便、无需溶剂、易于自动化操作等优点,近年来受到了国外学者的普遍关注,已经被用于环境分析和药品检测等许多领域,