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。     

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。     

Preparation and characterization of micro-bore wall-coated open-tubular capillaries with low phase ratios for fast-gas chromatography–mass spectrometry: Application to ignitable liquids and fire debris

Fast Gas Chromatography (GC) allows for analysis times that are a fraction of those seen in traditional capillary GC. Key modifications in fast GC include using narrow, highly efficient columns that can resolve mixtures using a shorter column length. Hence, a typical fast GC column has an inner diameter of 100–180 μm. However, to maintain phase ratios that are consistent with typical GC columns, the film thickness of fast GC stationary phases are also low (e.g., 0.1–0.18 μm). Unfortunately, decreased film thickness leads to columns with very low sample capacity and asymmetric peaks for analytes that are not sufficiently dilute. This paper describes micro-bore (50 μm i.d.) capillary columns with thick films (1.25 μm), and low phase ratios (10). These columns have greater sample capacity yet also achieve minimum plate heights as low as 110 μm. Hence, separation efficiency is much higher than would be obtained using standard GC columns. The capillary columns were prepared in-house using a simple static-coating procedure and their plate counts were determined under isothermal conditions. The columns were then evaluated using temperature programming for fast GC–MS analysis of ignitable liquids and their residues on fire debris exemplars. Temperature ramps of up to 75 °C min^?1 could be used and separations of ignitable liquids such as gasoline, E85 fuel, and lighter fluid (a medium petroleum distillate) were complete within 3 min. Lastly, simulated fire debris consisting of ignitable liquids burned on carpeting were extracted using passive headspace absorption-elution and the residues successfully classified.     

Sampling and recovery of ignitable liquid residues (ILRs) from fire debris using capillary microextraction of volatiles (CMV) for on-site analysis

A new, fast, and ultra-sensitive headspace sampling method using the Capillary Microextraction of Volatiles (CMV) device is demonstrated for the analysis of ignitable liquid residues (ILRs) in fire debris. This headspace sampling method involves the use of a heated can (60°C) to aid in the recovery of volatile organic compounds (VOCs) from medium and heavy petroleum distillates. Our group has previously reported the utility of CMV to extract gasoline at ambient temperature in less than 5 min in the field. This work evaluates the recovery and analysis of low mass loadings (tens of ng) of VOCs from charcoal lighter fluid, kerosene, and diesel fuel. Nonane, decane, undecane, tridecane, tetradecane, and pentadecane were selected for evaluation of recovery to represent these ILR classes. The face-down heated can headspace sampling technique was compared to the previously reported, non-heated, paper cup headspace sampling technique. Mass recovery improvements of 50%–200% for five of the six target compounds in diesel fuel were achieved compared to the non-heated sampling method. The average relative standard deviation (reported as % RSD) between the replicate trials decreased from an average of 28% to 6% when using the heated can method. Ignitable liquids were spiked onto burned debris in a live burn exercise and sampled using the heated can and paper cup headspace sampling techniques. The heated sampling technique reported here, for the first time, demonstrates an effective extraction method that when coupled to a portable GC–MS instrument allows for a sampling and analysis protocol in the field in less than 30 min.     

Direct and non-destructive proof of authenticity for the 2nd generation of Brazilian real banknotes via easy ambient sonic spray ionization mass spectrometry

Using a desorption/ionization technique, easy ambient sonic-spray ionization coupled to mass spectrometry (EASI-MS), documents related to the 2nd generation of Brazilian Real currency (R$) were screened in the positive ion mode for authenticity based on chemical profiles obtained directly from the banknote surface. Characteristic profiles were observed for authentic, seized suspect counterfeit and counterfeited homemade banknotes from inkjet and laserjet printers. The chemicals in the authentic banknotes' surface were detected via a few minor sets of ions, namely from the plasticizers bis(2-ethylhexyl)phthalate (DEHP) and dibutyl phthalate (DBP), most likely related to the official offset printing process, and other common quaternary ammonium cations, presenting a similar chemical profile to 1st-generation R$. The seized suspect counterfeit banknotes, however, displayed abundant diagnostic ions in the m/z 400–800 range due to the presence of oligomers. High-accuracy FT-ICR MS analysis enabled molecular formula assignment for each ion. The ions were separated by 44 m/z, which enabled their characterization as Surfynol® 4XX (S4XX, XX = 40, 65, and 85), wherein increasing XX values indicate increasing amounts of ethoxylation on a backbone of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (Surfynol® 104). Sodiated triethylene glycol monobutyl ether (TBG) of m/z 229 (C₁₀H₂₂O₄Na) was also identified in the seized counterfeit banknotes via EASI(+) FT-ICR MS. Surfynol® and TBG are constituents of inks used for inkjet printing.     

Prediction and preliminary standardization of fire debris constituents with the advanced distillation curve method

The recent National Academy of Sciences report on forensic sciences states that the study of fire patterns and debris in arson fires is in need of additional work and eventual standardization. We discuss a recently introduced method that can provide predicted evaporation patterns for ignitable liquids as a function of temperature. The method is a complex fluid analysis protocol, the advanced distillation curve approach, featuring a composition explicit data channel for each distillate fraction (for qualitative, quantitative, and trace analysis), low uncertainty temperature measurements that are thermodynamic state points that can be modeled with an equation of state, consistency with a century of historical data, and an assessment of the energy content of each distillate fraction. We discuss the application of the method to kerosenes and gasolines and outline how expansion of the scope of fluids to other ignitable liquids can benefit the criminalist in the analysis of fire debris for arson.     

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.     

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.     

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.     

The influence of the type of accelerant, type of burned material, time of burning and availability of air on the possibility of detection of accelerants traces

The presented research consisted in a series of field experiments and laboratory analyses of obtained samples. Their aim was to investigate how different factors influence the possibility of identification of accelerant traces in conditions that are as similar as possible to those of real fires. The studied factors were: type of burned material, type of accelerant, length of time between lighting and extinguishing of fire and the air availability level. The obtained results show that, among investigated factors, the type of burned material has the greatest influence. The other factors, with regard to their influence, could be ranked in descending order as follows: ‘other’ (hard to determine and regulate factors), type of accelerant, time of burning and air availability. ‘Other’ factors include arrangement of the burned material and dispersion of the accelerant.     

Combined target factor analysis and Bayesian soft-classification of interference-contaminated samples: Forensic Fire Debris Analysis

A Bayesian soft classification method combined with target factor analysis (TFA) is described and tested for the analysis of fire debris data. The method relies on analysis of the average mass spectrum across the chromatographic profile (i.e., the total ion spectrum, TIS) from multiple samples taken from a single fire scene. A library of TIS from reference ignitable liquids with assigned ASTM classification is used as the target factors in TFA. The class-conditional distributions of correlations between the target and predicted factors for each ASTM class are represented by kernel functions and analyzed by Bayesian decision theory. The soft classification approach assists in assessing the probability that ignitable liquid residue from a specific ASTM E1618 class, is present in a set of samples from a single fire scene, even in the presence of unspecified background contributions from pyrolysis products. The method is demonstrated with sample data sets and then tested on laboratory-scale burn data and large-scale field test burns. The overall performance achieved in laboratory and field test of the method is approximately 80% correct classification of fire debris samples.     

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.     

Hierarchical Cluster Analysis of Ignitable Liquids Based on the Total Ion Spectrum

Gas chromatography–mass spectrometry (GC–MS) data of ignitable liquids in the Ignitable Liquids Reference Collection (ILRC) database were processed to obtain 445 total ion spectra (TIS), that is, average mass spectra across the chromatographic profile. Hierarchical cluster analysis, an unsupervised learning technique, was applied to find features useful for classification of ignitable liquids. A combination of the correlation distance and average linkage was utilized for grouping ignitable liquids with similar chemical composition. This study evaluated whether hierarchical cluster analysis of the TIS would cluster together ignitable liquids of the same ASTM class assignment, as designated in the ILRC database. The ignitable liquids clustered based on their chemical composition, and the ignitable liquids within each cluster were predominantly from one ASTM E1618‐11 class. These results reinforce use of the TIS as a tool to aid in forensic fire debris analysis.     

Evaluation of Bluestar® Forensic Magnum and Other Traditional Blood Detection Methods on Bloodstained Wood Subjected to a Variety of Burn Conditions,

Accurate blood detection is a primary concern for forensic scientists, especially in highly compromised situations. In this study, blood was added to wood blocks and subjected to a variety of fire treatments: the absence or presence of accelerant, burn time (1, 3, or 5 min), and extinguishment method (smothering or dousing with water). Burned blocks were given a qualitative burn score, followed by removal of half of the char from each block and subsequent testing of each half for blood using luminol (13% positive; n = 96), Bluestar^® Forensic Magnum (5.2% positive; n = 96), and combined phenolphthalein tetramethylbenzidine test (0% positive; n = 192). Luminol and Bluestar® Forensic Magnum performed similarly, both outperforming PTMB. Additionally, positive results were more likely from samples that were smothered, had a low burn score, and had more concentrated blood solutions (neat or 1:2). Overall, it is extremely unlikely that blood would be detected on combustible substrates exposed to direct fire.     

The influence of the type of accelerant, type of burned material, time of burning and availability of air on the possibility of detection of accelerants traces

The presented research consisted in a series of field experiments and laboratory analyses of obtained samples. Their aim was to investigate how different factors influence the possibility of identification of accelerant traces in conditions that are as similar as possible to those of real fires. The studied factors were: type of burned material, type of accelerant, length of time between lighting and extinguishing of fire and the air availability level. The obtained results show that, among investigated factors, the type of burned material has the greatest influence. The other factors, with regard to their influence, could be ranked in descending order as follows: 'other' (hard to determine and regulate factors), type of accelerant, time of burning and air availability. 'Other' factors include arrangement of the burned material and dispersion of the accelerant.     

Evaluation of Cross‐contamination of Nylon Bags with Heavy‐loaded Gasoline Fire Debris and with Automotive Paint Thinner

Nylon bags are used for packaging fire debris in several countries, particularly in Europe. The possibility of cross‐contamination during transport from the fire scene to the laboratory, in normal casework conditions in the U.K., was studied for two brands of nylon bags, using simulated heavy‐loaded fire debris. Three experiments were carried out with each brand, using as sample a piece of cotton fabric soaked with gasoline. One experiment was carried out using automotive paint thinner (oxygenated solvent). Each sample was sealed in a nylon bag and stored in contact with eight empty bags. The empty bags were analysed at regular intervals for a period of time up to 8 weeks, using SPME and GC/MS. Cross‐contamination was found for components of gasoline (toluene and C₂‐alkylbenzenes) in the two brands of nylon bags used, after 4 days and 2 weeks. Cross‐contamination using automotive topcoat thinner was detected after 2 days.     

A comparison of extraction and adsorption methods for the recovery of accelerants from arson debris

Two different methods of recovering arson accelerants from fire debris are compared: distillation with addition of n-hexane and adsorption onto activated charcoal. Both procedures involve the use of the gas chromatography/mass spectrometry (GC/MS) utilizing specific mass ion programs. Some casework examples have been analyzed and the results show that, in spite of the advantages of short application times in the adsorption method, the distillation technique presented a higher degree of efficiency.     

Monitoring compliance to therapy during addiction treatments by means of hair analysis for drugs and drug metabolites using capillary zone electrophoresis coupled to time-of-flight mass spectrometry

Capillary electrophoresis coupled to time-of-flight mass spectrometry was used in the present work for the determination of therapeutic and abused drugs and their metabolites in the hair of subjects undergoing addiction treatments, in order to monitor their compliance to therapy. For this purpose a rapid, qualitative drug screening method was adopted based on capillary electrophoresis hyphenated with time-of-flight mass spectrometry, which had earlier been developed and validated for the forensic-toxicological analysis of hair, limitedly to illicit/abused drugs [1]. Sampling of hair was carried out in order to refer to a time window of about two months from the date of sampling (i.e. 2cm ca. from cortex). A single extraction procedure was applied, allowing the determination in the hair matrix of "drugs of abuse" referred to the past abuses, and therapeutic drugs prescribed in the detoxification program as well as their metabolites. Analyte identification was based on accurate mass measurements and comparison of isotope patterns, providing the most likely matching between accurate mass value and elemental formula. Small molecules (<500Da) of forensic and toxicological interest could be identified unambiguously using mass spectrometric conditions tailored to meet a mass accuracy ≤5ppm. In the present study, the proposed approach proved suitable for the rapid broad spectrum screening of hair samples, although needing further confirmation of results by using fragmentation mass spectrometry.     

Forensic analysis of ignitable liquids in fire debris by comprehensive two-dimensional gas chromatography

The application of comprehensive two-dimensional gas chromatography (GC x GC) for the forensic analysis of ignitable liquids in fire debris is reported. GC x GC is a high resolution, multidimensional gas chromatographic method in which each component of a complex mixture is subjected to two independent chromatographic separations. The high resolving power of GC x GC can separate hundreds of chemical components from a complex fire debris extract. The GC x GC chromatogram is a multicolor plot of two-dimensional retention time and detector signal intensity that is well suited for rapid identification and fingerprinting of ignitable liquids. GC x GC chromatograms were used to identify and classify ignitable liquids, detect minor differences between similar ignitable liquids, track the chemical changes associated with weathering, characterize the chemical composition of fire debris pyrolysates, and detect weathered ignitable liquids against a background of fire debris pyrolysates.