A review of the analysis of vegetable oil residues from fire debris samples: analytical scheme, interpretation of the results, and future needs

This paper reviews the literature on the analysis of vegetable (and animal) oil residues from fire debris samples. The examination sequence starts with the solvent extraction of the residues from the substrate. The extract is then prepared for instrumental analysis by derivatizing fatty acids (FAs) into fatty acid methyl esters. The analysis is then carried out by gas chromatography or gas chromatography-mass spectrometry. The interpretation of the results is a difficult operation seriously limited by a lack of research on the subject. The present data analysis scheme utilizes FA ratios to determine the presence of vegetable oils and their propensity to self-heat and possibly, to spontaneously ignite. Preliminary work has demonstrated that it is possible to detect chemical compounds specific to an oil that underwent spontaneous ignition. Guidelines to conduct future research in the analysis of vegetable oil residues from fire debris samples are also presented.     

Extraction, derivatization, and analysis of vegetable oils from fire debris

Vegetable oils have the ability to spontaneously heat under certain conditions, which may lead to spontaneous ignition. While the oils are not often encountered in forensic casework, they may be suspected in some fire cases. As these oils are not effectively analyzed using traditional fire debris analysis methods, a protocol must be established for extracting vegetable oils from fire debris. In this study, a protocol was developed for the extraction, derivatization, and analysis of vegetable oils from fire debris. Three derivatization methods were compared to establish an optimal derivatization procedure to convert the fatty acids found in vegetable oils to the fatty acid methyl esters (FAMEs) used in analysis. Three different gas chromatograph columns and programs were examined to determine which was best suited for the separation and analysis of FAMEs. The procedure was tested and refined using a variety of neat and burned vegetable oils, in addition to extractions from oils burned on commonly encountered fire debris materials. The findings of this research will serve as a starting point for further understanding and research of vegetable oils in fire debris.     

Practical Aspects of Analyzing Vegetable Oils in Fire Debris*

Abstract: Vegetable oils undergo burning, self‐heating, and spontaneous ignition, resulting in their presence in fire debris. As these processes can affect the fatty acid content of vegetable oils, it is important that debris be properly handled in order to obtain reliable and informative data. This research investigated changes in vegetable oil content as a result of storage conditions and different types of burning. Material spiked with vegetable oils and burned was stored under various long‐term conditions, and debris was tested by heating overnight using passive headspace concentration. Results indicated that refrigeration is ideal for fire debris samples suspected of containing vegetable oils and that including passive headspace concentration in the analytical scheme would not affect oils. Spontaneous ignition experiments were conducted to compare the effects of various burning processes on vegetable oil content. Vegetable oils that experienced nonpiloted ignition, self‐heating, and spontaneous ignition produced noticeably different chromatograms from those that underwent piloted ignition.     

Alternative fuels in fire debris analysis: biodiesel basics

Alternative fuels are becoming more prominent on the market today and, soon, fire debris analysts will start seeing them in liquid samples or in fire debris samples. Biodiesel fuel is one of the most common alternative fuels and is now readily available in many parts of the United States and around the world. This article introduces biodiesel to fire debris analysts. Biodiesel fuel is manufactured from vegetable oils and/or animal oils/fats. It is composed of fatty acid methyl esters (FAMEs) and is sold pure or as a blend with diesel fuel. When present in fire debris samples, it is recommended to extract the debris using passive headspace concentration on activated charcoal, possibly followed by a solvent extraction. The gas chromatographic analysis of the extract is first carried out with the same program as for regular ignitable liquid residues, and second with a program adapted to the analysis of FAMEs.     

Evaluation of the self-heating tendency of vegetable oils by differential scanning calorimetry

The evaluation of the self-heating propensity of a vegetable (or animal) oil may be of significant importance during the investigation of a fire. Unfortunately, iodine value and gas chromatographic-mass spectrometric analysis do not lead to meaningful results in this regard. To the contrary, differential scanning calorimetry (DSC), which does not measure the chemical composition of the oil, but rather its thermodynamic behavior, produces valuable results. After a thorough literature review on the autooxidation of vegetable oils, several oils with different self-heating tendencies were analyzed using a Mettler-Toledo differential scanning calorimeter DSC 25 between 40 degrees C and 500 degrees C. Analyses were carried out both under air and nitrogen atmosphere to identify the phenomena due to autooxidation reactions. Using DSC, it was possible to observe the induction period of the oil (when available), the three different exothermic events, and the autoignition temperature (relatively independent of the oil type).     

Analysis and classification of common vegetable oils

The analysis of fatty acids from common vegetable oils was investigated for application to forensic casework. A base-catalyzed transesterification of the fatty acids to fatty acid methyl esters using tetramethylammonium hydroxide was simple, rapid, straightforward and inexpensive. Canola, corn, olive, peanut, safflower, soybean and sunflower oils were able to be classified based on their fatty acid methyl ester profiles. Using gas chromatography-mass spectrometry, the detection limits for canola, corn, olive, peanut and safflower oils were determined to be 0.4 mg/mL or less and 0.2 mg/mL or less for soybean and sunflower oils.     

A method for forensic identification of vegetable oil stains--rapid analysis of carboxylic acids with methyl esterification using purge-and-trap gas chromatography/mass spectrometry.

A simple method using purge-and-trap gas chromatography/mass spectrometry (P&T-GC/MS) for forensic examination of oil stains was studied. Carboxylic acids, chosen as target components for discrimination of oil samples, were extracted from stains with ether, methyl esterified by tetramethylammonium hydroxide, and analyzed by P&T-GC/MS. Vegetable oils were discriminated according to their carboxylic acid compositions. Carboxylic acid composition was independent of the substrate material of the stain. Although the carboxylic acid composition of the oil changed on exposure to sunlight, identification of oil was possible for oil stains that had been in the shade, if analysis was made within 20 days.     

纵火现场中汽油、煤油和柴油残留物的ATD／GC／MS法检测

目的为火场中汽油、煤油和柴油残留物的检测建立一种简便、高灵敏度的ATD／GC／MS检验方法。方法采用Tenax TA吸附管吸附富集检材中的汽油、煤油和柴油成分。然后用美国PE公司的ATD／GC／MS仪器进行全自动的解吸和分析检测。结果检材中汽油、煤油和柴油的检测极限分别达0．05、0.2、0．2pL／mL。结论该方法具解吸和分析检测过程自动化。操作简便快捷，检测灵敏度高。杂质干扰少等特点，可用于实际火场皆汽油、煤油和柴油残留物的检测。     

同时裂解甲基化气相色谱法快速鉴别人体脂肪及动植物油脂

采用同时裂解甲基化气相色谱法（SPM－GC），首次分析人体脂肪，并且观察人体脂肪、猪、鸡、牛、羊脂和豆油中7种脂肪酸的组份含量变化。根据7种主要脂肪酸（肉豆蔻酸、棕榈酸、棕榈油酸、硬脂酸、油酸、亚油酸和亚麻酸）甲酯的百分含量可有效地进行鉴别。结果表明：通过SPM－GC法分析油脂，可将传统的油脂酯化法时间由2个多小时缩短到1分钟左右。数据C．V．％＜4％，最小检测量为1．Oμg。最佳比例四甲基氢氧化按（TMAH）甲醇液（TMAH：甲醇＝1：10，V／V），可消除油脂中多不饱和脂肪酸的异构化和降解。     

The Effects of Burning and Mold Growth on the Chemical Composition of Firelog Fuels

Firelogs consist of a cellulosic material, such as sawdust or wood particles, and a combustible binder (fuel). Historically, the fuel typically consisted of a petroleum‐based (paraffin) wax; however, some manufacturers now include vegetable oils in their firelog fuels. To determine fuel composition, fuels from various brands of firelogs were extracted and analyzed by high‐temperature gas chromatography–mass spectrometry (HTGC‐MS) and a GC‐MS with a polar column specific for the analysis of fatty acid methyl esters (FAMEs). Firelogs were also burned, allowed to grow mold, and analyzed by GC‐MS to determine the effects that burning and mold growth have on firelog fuel composition. Mold did not tend to preferentially degrade any of the fatty acids. Burning caused a decrease in the relative amount of all of the fatty acids present in the vegetable oil fuel, with a greater effect on unsaturated fatty acids than saturated ones.     

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。     

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。     

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.     

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。     

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。     

Extraction of alternative fuels from fire debris samples*

Alternative fuels, specifically biodiesel, biodiesel blends, and E85 fuel, have been gaining a market share over the past few years. With the emergence of these fuels, fire debris analysts should be able to recognize their characteristics since these fuels may be encountered in casework. In this study, pure biodiesel (B100) and a 20% blend of pure biodiesel with petroleum diesel (B20) are examined as liquids and are extracted from debris samples using both passive headspace concentration and solvent extraction. Typical fire debris instrumental conditions are used to analyze these samples. Components of B100 and B20 may be observed in debris samples extracted using the passive headspace concentration method, but the chromatographic patterns are different from the pure liquid samples. When solvent extraction is used as a secondary extraction method on debris samples, the resulting patterns are consistent with the pure liquids of B100 and B20. E85 fuel, a blend of 85% ethanol and 15% gasoline, can be extracted using a typical fire debris extraction technique but requires slight modifications to typical fire debris instrumental conditions. E85 is shown at various stages of evaporation to demonstrate the resiliency of the ethanol. Additionally, samples of E85 were placed on carpet, burned and extinguished to demonstrate the effects of the suppression medium on the retention of ethanol.     

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.     

Forensic Identification of Seal Oils Using Lipid Profiles and Statistical Models

Seal blubber oils are used as a source of omega‐3 polyunsaturated fatty acids in Canada but prohibited in the United States and (FA) European Union. Thus, a reliable method is needed to identify oils originating from seals versus fish. Two lipid profiling methods, fatty acid analysis using gas chromatography and triacylglycerol (TAG) analysis using liquid chromatography and mass spectrometry, were applied with statistical models to discriminate commercial oils and blubber samples harvested from marine fish and seals. Significant differences were observed among FA profiles, and seal samples differed from each of the fish oils (p ≤ 0.001). FA and TAG profiles were used to discriminate sample groups using a random forest classifier; all samples were classified correctly as seals versus fish using both methods. We propose a two‐step method for the accurate identification of seal oils, with preliminary identification based on FA profile analysis and confirmation with TAG profiles.     

Progress Toward the Determination of Correct Classification Rates in Fire Debris Analysis,,

Principal components analysis (PCA), linear discriminant analysis (LDA), and quadratic discriminant analysis (QDA) were used to develop a multistep classification procedure for determining the presence of ignitable liquid residue in fire debris and assigning any ignitable liquid residue present into the classes defined under the American Society for Testing and Materials (ASTM) E 1618‐10 standard method. A multistep classification procedure was tested by cross‐validation based on model data sets comprised of the time‐averaged mass spectra (also referred to as total ion spectra) of commercial ignitable liquids and pyrolysis products from common building materials and household furnishings (referred to simply as substrates). Fire debris samples from laboratory‐scale and field test burns were also used to test the model. The optimal model's true‐positive rate was 81.3% for cross‐validation samples and 70.9% for fire debris samples. The false‐positive rate was 9.9% for cross‐validation samples and 8.9% for fire debris samples.     

The use of vapour phase ultra-violet spectroscopy for the analysis of arson accelerants in fire scene debris.

A method has been developed for the analysis of arson accelerants in fire scene debris by vapour phase ultra-violet (UV) spectroscopy. The method is rapid, inexpensive, simple to use and is sufficiently sensitive and discriminating to be of use for the analysis of crime scene samples. Application to casework samples is described. On occasion, the method offers additional information to that which can be obtained by gas chromatography-flame ionisation detection (GC-FID) and gas chromatography-mass spectrometry (GC-MS) and represents a useful adjunct to these techniques. In addition, the method offers advantages where the use of GC-MS analysis of arson accelerants in fire scene debris is not a practical proposition.