A solid-phase microextraction method for the detection of ignitable liquids in fire debris

A solid-phase microextraction (SPME) procedure involving direct contact between the SPME fibers and the solid matrix and subsequent gas chromatography/mass spectrometric analysis for the detection of accelerants in fire debris is described. The extraction performances of six fibers (100 mum polydimethylsiloxane, 65 mum polydimethylsiloxane-divinylbenzene, 85 mum polyacrylate, 85 mum carboxen-polydimethylsiloxane, 70 mum Carbowax-divinylbenzene, and 50/30 mum divinylbenzene-Carboxen-polydimethylsiloxane) were investigated by directly immersing the fibers into gasoline, kerosene, and diesel fuel. For simulated fire debris, in the direct contact extraction method, the SPME fiber was kept in contact with the fire debris matrix during extraction by penetrating plastic bags wrapping the sample. This method gave comparable results to the headspace SPME method in the extraction of gasoline and kerosene, and gave an improved recovery of low-volatile components in the extraction of diesel fuel from fire debris. The results demonstrate that this procedure is suitable as a simple and rapid screening method for detecting ignitable liquids in fire debris packed in plastic bags.     

火场样品中汽油与稀释剂燃烧残留物的区分方法探讨

目的探讨火场样品中汽油与稀释剂燃烧残留物的区分方法。方法样品用ATD—GC—MS法检验,检验结果通过对芳烃、烷烃、茚满、和萘系列的4个特征离子色谱图与已知汽油和稀释剂作比较,并结合向量夹角法计算样品与汽油色谱指纹图的相似度来区分汽油与稀释剂残留物。结果个别品种的稀释剂燃烧残留物与汽油很相似,但彼此有某些差别。结论使用本方法,一般能将汽油与稀释剂燃烧残留物区分开。     

Using Alkylate Components for Classifying Gasoline in Fire Debris Samples

The characteristic that discriminates gasoline from other ignitable liquids is that it contains high‐octane blending components. This study elaborates on the idea that the presence of gasoline in fire debris samples should be based on the detection of known high‐octane blending components. The potential of the high‐octane blending component alkylate as a characteristic feature for gasoline detection and identification in fire debris samples is explored. We have devised characteristic features for the detection of alkylate and verified the presence of alkylate in a large collection of gasoline samples from petrol stations in the Netherlands. Alkylate was detected in the vast majority of the samples. It is demonstrated that alkylate can be detected in fire debris samples that contain traces of gasoline by means of routine GC‐MS methods. Detection of alkylate, alongside other gasoline blend components, results in a more solid foundation for gasoline detection and identification in fire debris samples.     

建立火场样品中汽油残留物ATD-GC-MS检验结果的评价方法

目的建立火场中汽油燃烧残留物ATD-GC-MS检验结果评价方法。方法将模拟燃烧样品用ATD-GC-MS法检验,检验结果通过对芳烃、烷烃、茚满、和萘系列的4个特征离子色谱图与已知汽油作比较,并利用向量夹角法计算样品与汽油色谱指纹图的相似度来对检验结果作评价。结果有汽油作助燃剂的模拟燃烧样品与汽油色谱指纹图的相似度一般大于90%,无汽油作助燃剂的样品则在60%以下。结论利用样品的4个特征离子色谱图与已知汽油作比较,并结合样品与汽油色谱指纹图相似度的计算,能对检验结果作出客观、可靠和准确的评价。     

Use of a solid absorbent and an accelerant detection canine for the detection of ignitable liquids burned in a structure fire

ABSTRACT: Ignitable Liquid Absorbent^™ (ILA), a commercial solid absorbent intended to assist fire scene investigators in sample location and collection, has been field tested in three separate room fires. The ability of the ILA to detect and absorb different amounts of gasoline, odorless paint thinner, and camp fuel on two different substrates after a full-scale burn was assessed against results from an accelerant detection canine and laboratory analysis using gas chromatography-mass spectrometry (GC-MS). The canine correctly alerted on most of the panels that contained an ignitable liquid after the fire, while the ILA indicator dye failed to indicate in the presence of gasoline and camp fuel. GC-MS results for ignitable liquid residue from each panel and from the ILA showed that ILA absorbed odorless paint thinner and camp fuel from most of the test panels, but failed to absorb gasoline from the panels on which gasoline was confirmed to be present.     

Progress Toward the Determination of Correct Classification Rates in Fire Debris Analysis II: Utilizing Soft Independent Modeling of Class Analogy (SIMCA)

A multistep classification scheme was used to detect and classify ignitable liquid residues in fire debris into the classes defined by the ASTM E1618‐10 standard method. The total ion spectra (TIS) of the samples were classified by soft independent modeling of class analogy (SIMCA) with cross‐validation and tested on fire debris. For detection of ignitable liquid residue, the true‐positive rate was 94.2% for cross‐validation and 79.1% for fire debris, with false‐positive rates of 5.1% and 8.9%, respectively. Evaluation of SIMCA classifications for fire debris relative to a reviewer's examination led to an increase in the true‐positive rate to 95.1%; however, the false‐positive rate also increased to 15.0%. The correct classification rates for assigning ignitable liquid residues into ASTM E1618‐10 classes were generally in the range of 80–90%, with the exception of gasoline samples, which were incorrectly classified as aromatic solvents following evaporative weathering in fire debris.     

Comparison of gasolines using gas chromatography-mass spectrometry and target ion response

Gas chromatography-mass spectrometry was used to compare gasoline samples obtained from different sources based on the difference in amounts of certain components found in the headspace of gasoline using target response data. Many suspected arson cases involve comparing an ignitable liquid extracted from fire debris to a liquid found in a suspect's possession to determine if they could have had a common source. Various component ratios are proposed for determining if an unevaporated gasoline sample could have originated from the same source as an evaporated gasoline extracted from fire debris. Fifty and 75% evaporated gasoline samples were both found to contain similar ratios of certain components when compared with its unevaporated source gasoline. The results of the comparisons in this study demonstrate that for cases involving gasoline that has been evaporated up to 50% and extracted from pine, it is possible to eliminate comparison samples as originating from the same source. The results of the 75% comparisons suggest it may be possible to apply the same type of comparison to cases involving 75% evaporated gasoline.     

Effect of evaporation and matrix interferences on the association of simulated ignitable liquid residues to the corresponding liquid standard

Identification of an ignitable liquid in fire debris evidence can be complicated due to evaporation of the liquid, matrix interferences, and thermal degradation of both the liquid and the matrix. In this research, liquids extracted from simulated fire debris were compared to the original liquid using multivariate statistical procedures. Neat and evaporated gasoline and kerosene standards were spiked onto nylon carpet, which was subsequently burned. The ignitable liquid residues were extracted using a passive headspace procedure and analyzed by gas chromatography-mass spectrometry. Pearson product moment correlation coefficients, hierarchical cluster analysis, and principal components analysis were used to compare the liquids extracted from the carpet to the corresponding neat liquid. For each procedure, association of the extracts according to liquid type was possible, albeit not necessarily to the specific evaporation level. Of the three procedures investigated, principal components analysis offered the most promise since contributions from matrix interferences were essentially eliminated.     

Performance Testing of the New AMPAC Fire Debris Bag Against Three Other Commercial Fire Debris Bags(*)

Abstract: Fire debris evidence is collected and stored in a wide range of containers, including various polymer bags. Four different polymer bags have been investigated, including the NYLON, DUO, ALU, and AMPAC bags. The latter is the successor of the Kapak Fire DebrisPAK^?. Microscopy and infrared spectroscopy were used to elucidate the composition of the bags. Gas chromatography/mass spectrometry was used to investigate performance parameters such as background volatiles, leak rate, cross‐contamination, recovery, and sorption. The NYLON bag was susceptible for leakage and cross‐contamination and showed decreased recoveries. The DUO and ALU bags showed some background volatiles, sorption, and poor recoveries. The AMPAC bag performed excellent: low background, no leakage or cross‐contamination, good recoveries, and only traces of sorption. Heat sealing proved to be the best method of closure. Preliminary studies on AMPAC bags showed that polyethylene clamps are easy to use on‐site and preserve ignitable liquids adequately for a limited period of time.     

Evaluation of a Headspace Solid‐Phase Microextraction Method for the Analysis of Ignitable Liquids in Fire Debris

The chemical analysis of fire debris represents a crucial part in fire investigations to determine the cause of a fire. A headspace solid‐phase microextraction (HS‐SPME) procedure for the detection of ignitable liquids in fire debris using a fiber coated with a mixture of three different sorbent materials (Divinylbenzene/Carboxen/Polydimethylsiloxane, DVB/CAR/PDMS) is described. Gasoline and diesel fuel were spiked upon a preburnt matrix (wood charcoal), extracted and concentrated with HS‐SPME and then analyzed with gas chromatography/mass spectrometry (GC/MS). The experimental conditions—extraction temperature, incubation and exposure time—were optimized. To assess the applicability of the method, fire debris samples were prepared in the smoke density chamber (SDC) and a controlled‐atmosphere cone calorimeter. The developed methods were successfully applied to burnt particleboard and carpet samples. The results demonstrate that the procedure that has been developed here is suitable for detecting these ignitable liquids in highly burnt debris.     

GC/MS/MS时间编程在火灾现场助燃剂检测中的应用

运用Varian SATURN2000气质联用仪通过GC/MS、GC/MS/MS、时间编程 GC/MS/MS对汽油样品进行分析比对,发现利用时间编程GC/MS/MS,对检测火灾现场残留汽油效果很好,可彻底排除样品中基体的背景干扰,大大提高检测灵敏度;同时对混合助燃剂（汽油+煤油、汽油+柴油）进行了实验探索。     

The evaluation of the extent of transporting or "tracking" an identifiable ignitable liquid (gasoline) throughout fire scenes during the investigative process

Tests have determined that boots or shoes of individuals at a fire scene do not transport sufficient contaminants ("tracking") through the fire scene to produce a positive laboratory result for the presence of gasoline in a fire scene that was not present at the time of the fire. Questions about the validity of forensic laboratory results have been raised on the basis that low-level gasoline residues detected in the laboratory samples could have been the result of transporting the residue by footwear contaminated from the fire scene ("tracking"). The data collected in this study establish that "tracking" does not lead to false-positive laboratory results. Canines trained and experienced in the detection of trace ignitable liquid residues were also utilized in this study. The canine results confirmed that properly trained canines show a higher sensitivity than do standard ASTM laboratory techniques for fire debris analysis. In a few cases, canines responded to contamination, but laboratory testing (which is the definitive indicator) did not produce positive results.     

Comparison of new Ampac bags and FireDebrisPAK® bags as packaging for fire debris analysis

Abstract: The FireDebrisPAK^® bags that were produced by Kapak were considered to be one of the best containers for fire debris. Kapak bags were discontinued; however, from July 2010, Ampac is offering a new packaging material. The aim of the presented research was to compare the properties (durability, background interferences, and permeability) of Kapak bags and packaging material offered by Ampac. The analysis was conducted by passive adsorption from the headspace with subsequent thermal desorption and analysis by GC‐MS. The results proved that the properties of the compared materials are similar. Their greatest advantage is that they are impermeable for components of flammable liquids, so there is no danger of losing analytes or cross‐contamination. Their one significant drawback is that they should not be exposed to temperatures above 80°C. At this temperature, they become soft, their inner layer is compromised (becomes sticky), and they emit some volatile organic compounds. Among them, there are compounds that constitute the components of some of flammable liquids.     

Determining the Method Threshold of Identification via Gas Chromatography–Mass Spectrometry of Weathered Gasoline Extracted from Burnt Nylon Carpet,

The Organization of Scientific Area Committees defines threshold of identification as the minimum concentration of ignitable liquid identifiable from gas chromatographic‐mass spectrometry data using accepted pattern identification criteria. We propose a method for determining this threshold for gasoline based on base peak to qualifier ratios of six compounds. The ion ratios were established for each compound in the neat gasoline. These ratios were then compared to those obtained for gasoline and 98% weathered gasoline both spiked onto burnt nylon carpet at 20 ppt down 0.50 ppt, and recovered from the carpet using headspace extraction (ASTM 1412). Identification was confirmed if the compounds’ ion ratios fell within ±25% of that in the neat sample. We found that ion ratios for all samples were acceptable for six compounds at 1.60 and 0.80 ppt for extracted neat and extracted 98% weathered gasoline, respectively, illustrating potential for incorporating into Quality Assurance Programs.     

ATD—GC—MS法测定火场样品中痕量汽油燃烧残留物

目的为火场样品中痕量汽油残留物的检测建立一种简便、高灵敏度的检验方法和可靠的检验结果评判方法。方法用TenaxTA吸附管吸附富集火场样品中的汽油成分,然后用ATD—GC—MS法自动解吸和检测。通过模拟燃烧实验,探讨了检验结果的评判方法：根据样品的m／z（57＋85）、m/z（91＋105＋119）、m／z（117＋131）和m/z（128＋142＋156）四个质量色谱图与已知汽油作比较来对检验结果作评判。结果6组模拟燃烧实验中凡有汽油作助燃剂的样品．均检出汽油残留物成分。结论所建立的方法具有操作简便,检测灵敏度高,杂质干扰少,定性结论准确可靠等特点。可用于实际火场样品中痕量汽油残留物的检测。     

自动热脱附气相色谱-质谱法分析火场助燃剂汽油成分

目的建立检验纵火案件现场燃烧残留物中助燃剂汽油成分的方法。方法利用自动热脱附技术对火场残留物中的助燃剂进行富集、浓缩、脱附后经气-质联用仪（GG-MS）分析。结果结合现场燃烧环境运用目标化合物法能够判定是否含有助燃剂汽油成分。结论该方法简便易行。     

Forensic Comparison of Automotive Aluminum Wheel Fragments Using Synchrotron Radiation X‐ray Fluorescence with 18‐ and 116‐keV Excitation X‐rays

The performance of synchrotron radiation X‐ray fluorescence (SR‐XRF) spectrometry for nondestructive discrimination of small fragments of automotive aluminum wheels was studied. Fragments (< 500 × 500 μm²) of 45 kinds of wheels were first analyzed by scanning electron microscopy–energy dispersive spectroscopy (SEM‐EDS) and then by SR‐XRF. Despite the Mg/Al intensity ratio being a useful identification index, SEM‐EDS was not efficient enough because of the absence of other meaningful indicators of comparison. Conversely, pairwise comparison was conducted and a 92.9% identification was achieved via SR‐XRF using 18‐keV X‐rays. Trace heavy elements in the high‐energy region were detected by SR‐XRF using 116‐keV X‐rays, and an 82.9% identification was obtained. Combined use of 18‐ and 116‐keV X‐rays allowed 98.2% identification. Hence, SR‐XRF is a powerful tool for nondestructive discrimination of automotive aluminum wheels with high precision using trace elements in a wide energy region.     

Trace Elemental Analysis of Titanium Dioxide Pigments and Automotive White Paint Fragments for Forensic Examination Using High‐Energy Synchrotron Radiation X‐Ray Fluorescence Spectrometry*

Abstract: High‐energy synchrotron radiation x‐ray fluorescence spectrometry (SR‐XRF) utilizing 116 keV x‐rays was used to characterize titanium dioxide pigments (rutile) and automotive white paint fragments for forensic examination. The technique allowed analysis of K lines of 9 trace elements in 18 titanium dioxide pigments (rutile), and 10 trace elements in finish coat layers of seven automotive white paint fragments. High‐field strength elements (HFSE) were found to strongly reflect the origin of the titanium dioxide (TiO₂) pigments, and could be used as effective parameters for discrimination and classification of the pigments and paint fragments. A pairwise comparison of the finish coat layers of seven automotive white paint fragments was performed. The trace elements in the finish coat layers detected by the high‐energy SR‐XRF were especially effective for identification. By introducing the trace element information of primer and electrocoat layers, all the automotive white paint fragments could be discriminated by this technique.     

Pyrolysis Products of Linear Alkylbenzenes— Implications in Fire Debris Analysis*

Abstract: In this case report, potential interferences from an improvised fire‐extinguishing agent, a dishwashing liquid, containing linear alkylbenzene sulfonates (LAS), was studied. The presence of linear alkylbenzenes (LABs) in the fire debris sample was identified from the summed ion profile (SIP) analysis. It was found that the LAS from dishwashing liquids produce LABs by thermal degradation. Direct pyrolysis of a LAS‐containing dishwashing liquid at 300°C yielded a distribution of LABs in the SIP. LABs began to break down at pyrolysis temperatures between 450 and 500°C and completely break down by 800°C. Observed pyrolysis breakdown products of LABs included toluene, ethylbenzene, meta‐, para‐, and ortho‐xylenes, propylbenzene, indane, naphthalene, and 1‐ and 2‐methylnaphthalenes. These data suggested the presence of LABs in fire debris evidence might complicate subsequent analysis because their breakdown products contained some of the target compounds common to ignitable liquid identification. Therefore, a positive determination of the presence of foreign ignitable liquids should be carefully evaluated when there is a presence of LABs in the SIP.     

Compositional analysis for identification of arson accelerants by electron ionization Fourier transform ion cyclotron resonance high-resolution mass spectrometry

Elemental compositions of each of 100 to 500 different constituents (i.e., every peak in a mass-to-charge ratio range, 50 < m/z < 300) of lighter fluid, kerosene, turpatine, gasoline, diesel fuel, and two brands of mineral spirits (and their weathered analogs) make possible direct identification of each accelerant in a experimental fire, based on electron ionization 6.0 Tesla Fourier transform ion cyclotron resonance (EI FT-ICR) ultrahigh resolution mass spectrometry. Septum injection of as little as 500 nL of accelerant into an all-glass heated inlet system yields definitive elemental compositions (molecular formulas) based on accurate (< +/-1 ppm average error) mass measurement alone. Extraction and EI FT-ICR mass analysis of fire debris from a controlled burn of a couch with simple (lighter fluid) and complex (turpatine) ignitable liquid yielded dozens of elemental compositions serving as a unique "fingerprint" for each petroleum product, despite the presence of up to 249 additional extracted matrix and pyrolysis components. Forty-five of 56 lighter fluid constituents and 126 of 133 turpatine constituents (not counting 13C-containing species) were identified in the debris from a fire staged for each respective accelerant.