Passive Headspace Concentration Research Articles

The effects of F-500 Encapsulator Agent on canine alerts and laboratory analysis using passive headspace concentration and gas chromatography-mass spectrometry

F-500 Encapsulator Agent (EA) is a fire suppression agent that is an alternative to traditional firefighting foams. It is marketed as having the capability to act on all four parts of the fire tetrahedron as well as being environmentally friendly and non-toxic. An internal survey of the use of F-500 EA by fire departments encountered by the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) ignitable liquid detection canine (ILDC) handlers in 2022 showed that this product is not yet in widespread use across the country, but where it has been implemented, it is frequently utilized on a variety of types of fires. Additional agencies are researching the product to determine if it should be adopted. As this product appears to be growing in popularity, it is important to understand whether the use of the product would affect a canine’s ability to detect ignitable liquids or a forensic laboratory’s ability to identify the presence of an ignitable liquid. Burned wood and burned carpet, two commonly encountered substrates, were spiked with gasoline or a heavy petroleum distillate (HPD) and F-500 EA was applied. At various time intervals, ILDC teams surveyed the samples and laboratory analysis was conducted. Results showed that the presence of F-500 EA can negatively affect canine alerts and the laboratory’s ability to identify ignitable liquids.

Dynamic vapor microextraction of ignitable liquid from casework containers

Dynamic vapor microextraction (DVME) is a headspace concentration method that can be used to collect ignitable liquid (IL) from fire debris onto chilled adsorbent capillaries. Unlike passive headspace concentration onto activated carbon strips (ACSs) that must be eluted with a toxic solvent (carbon disulfide), DVME employs a relatively benign solvent (acetone) to recover the adsorbed IL residue, and each headspace collection is monitored for breakthrough. Here, for the first time, we extend DVME to casework containers while exploring a realistic range of oven temperatures and collection volumes. We investigated metal cans sealed with friction lids (container 1), metal cans sealed within polymer bags (container 2), and glass jars sealed with two-piece lids (container 3). Without additional containment, container 1 was found to leak so excessively that flow through the capillary was unreliable. Therefore, for containers 2 and 3 only, we determined the total number of target compounds collected from 50% weathered gasoline for oven temperatures from 54 °C to 96 °C and collection volumes from 47 standard cubic centimeters (scc) to 90 scc. Only high-volatility species with retention times (tR)< n-decane on a non-polar column were recovered from polymer bags, whereas headspace concentration from glass jars led to the recovery of target compounds across the entire volatility range. DVME at 90 °C from 2-mL containers showed that the presence of polymer bag material leads to IL vapor losses, particularly for low-volatility species with tR> n-decane. DVME was strongly influenced by the casework container, whereas oven temperature and collection volume had a minor influence for the IL samples explored here.

Characterization of a headspace sampling method with a five-component diesel fuel surrogate

PLOT-cryoadsorption concentrates headspace vapors by sweeping them through porous layer open tubular (PLOT) capillaries chilled to 0 °C to promote adsorption onto an alumina layer. Compared to passive headspace concentration employing activated charcoal strips (ACSs) as adsorbents, PLOT-cryoadsorption has several potential advantages for extracting ignitable liquid (IL) residue from fire debris evidence. Capillary vapor traps can be monitored for breakthrough to avoid problematic displacement that occurs when an adsorbent becomes saturated. Capillaries can also be eluted with acetone to avoid highly toxic carbon disulfide. Future adoption of PLOT-cryoadsorption for fire debris analysis requires investigation of sampling parameters including collection volume, flow rate, and temperature. Here we employ a simple five-component surrogate for diesel fuel (that is, a simulated or artificial diesel fuel) to study the effect of flow rate and sample temperature on the composition and spatial distribution of the collected headspace. Flow rates at or below 1.5 scc (standard cubic centimeters)/min yielded the most repeatable results. Across the range 60 °C to 120 °C, we found that high sample temperatures allowed for the collection of more total sample and shifted its composition towards lower-volatility components. Consistent with chromatographic theory, higher-volatility components traveled furthest along the length of the capillary and were more prone to breakthrough. We conclude that the surrogate mixture allowed for effective, quantitative comparisons between sampling conditions that could be translated to real diesel fuel.

The use of hydrophobic pads to recover ignitable liquids from water

Significant amounts of water are used to extinguish fires, and finding evidence of ignitable liquid residue can be challenging for investigators. Hydrophobic pads have been designed to collect oil-based products from the surface of water and preferentially absorb non-polar compounds while repelling water. In this study hydrophobic pads are used to collect various classifications of ignitable liquids from the surface of water for analysis using passive headspace concentration and GC/MS analysis. Hydrophobic pads were found to be effective in collecting ignitable liquids containing hydrocarbons greater than C8, classifications medium and heavy petroleum distillates, from 10 microliters of ignitable liquids added to the surface of 100 milliliters of water. Gasoline and 50% evaporated gasoline were also recovered using the hydrophobic pads with 25 microliters of sample.

Evaluation of long term preservation of ignitable liquids adsorbed onto charcoal strips: 0 to 2 years

Activated charcoal strips (c-strips) are routinely used to preserve volatile components extracted from fire debris. This study sought to evaluate the use of c-strips for long term sample preservation. Gasoline or a heavy petroleum distillate was spiked at low and high spike volumes in triplicate, then extracted using passive headspace concentration. Extracts were stored in three types of vials: 2-mL screw cap gas chromatography (GC) vials, 2-mL crimp cap GC vials, and 4-mL screw cap vials. To evaluate persistence, c-strips were stored at room temperature then eluted at multiple time intervals: 0 days (immediately following extraction), 10 days, 1 month, 6 months, 1 year, and 2 years. Gasoline and the heavy petroleum distillate at both spike volumes were identifiable for all replicates for the full two-year period, for each storage vial type tested. This demonstrates that c-strips are effective for the long-term preservation of ignitable liquids.

The potential interference of body products and substrates to the identification of ignitable liquid residues on worn clothing

The question of whether deposits on clothing as well as their chemical composition are being mistaken for ignitable fluids is a concern for forensic analysts. Body products and oil secretions can have similar chemical profiles to ignitable liquid residues (ILRs) as a result of comparable chemical compounds that may be found in both sources. This study investigated whether substrates of unworn and worn clothing, with endogenous body secretions and body products could interfere with ILR analysis. Sample extraction was completed by passive headspace concentration with activated charcoal strips (ACS) and desorption with carbon disulfide followed by analysis with gas chromatography-mass spectrometry (GC–MS). Results showed that some body products produce similar patterns to heavy petroleum distillates and most clothing contained components that are commonly found in ignitable liquids. It was concluded that the clothing, body products and compounds released by the body all contribute to the GC–MS profile of worn clothing. These components can mimic or mask the presence of ILRs, however educated and experienced analysts would likely be able to differentiate these substrate patterns from ILRs.

Biodegradation of representative ignitable liquid components on soil

A mixture containing 14 hydrocarbons representing six distinct compound types (e.g. normal alkanes, branched alkanes, cyclic alkanes, aromatics, polynuclear aromatics, and oxygenates) was deposited onto ninety grams of potting soil and allowed to remain for specified periods of time. Hydrocarbons remaining at the end of each time period were extracted by passive headspace concentration and analyzed by gas chromatography-mass spectrometry. No byproducts were observed to be formed or accumulate during biodegradation in this study. There was sizable loss of oxygenated compounds, normal alkanes, and toluene compared to poly-substituted aromatics, polynuclear aromatics, branched alkanes, and cyclic alkanes. The half-life for the cumulative loss of all components of the hydrocarbon mixture was calculated to be 3.15days. A half-life as short as 1.75days was determined for the integrated loss of a commercial ignitable liquid from the ASTM E1618 aromatic class ignitable liquid.

Collection and analysis of fire debris evidence to detect methamphetamine, pseudoephedrine, and ignitable liquids in fire scenes at suspected clandestine laboratories

The “One Pot” methamphetamine production method uses highly reactive and flammable materials. Clandestine laboratories created using this method may lead to subsequent fires putting innocent bystanders at risk. In some jurisdictions, fires resulting from methamphetamine production may lead to first degree arson charges, which have much higher penalties than drug production charges. The ability to detect methamphetamine and precursors in fire debris provides necessary evidence to charge first degree arson. In this study, One Pot methamphetamine reactions were used to create mock residential fires. Debris samples were analyzed for ignitable liquids using passive headspace concentration and gas chromatography-mass spectrometry. Liquid chromatography-tandem mass spectrometry was then used to detect methamphetamine and pseudoephedrine, the methamphetamine precursor, in the fire debris. Additionally, samples were provided to local law enforcement laboratories for standard drug analysis. This work demonstrates the positive identification of both ignitable liquids and the drugs/precursors from fires resulting from clandestine methamphetamine production.

Validation of an HS-MS method for direct determination and classification of ignitable liquids

Fire debris analysis is a key step in fire investigation. Most of the analytical methods used for the analysis of ignitable liquid residues in fire debris require pre-concentration of the ignitable liquid residues prior to the chromatographic analysis. The standard method, ASTM E1412, involves a passive headspace concentration with activated charcoal strips to isolate the ignitable liquid residues from fire debris followed by a desorption procedure from the carbon strip with carbon disulfide.In this study a non-separative analytical method based on HS-MS eNose (headspace mass spectrometry electronic nose) in combination with chemometric tools, including hierarchical cluster analysis and linear discriminant analysis, has been used to detect and classify ignitable liquid residues in fire debris into the classes defined by the ASTM E1618 standard method. This method allows a direct analysis of fire debris in 10min and avoids the use of solvent and sorbents.The method was validated by analyzing a set of burned samples by GC–MS according to the standard methods ASTM E1412 and ASTM E1618. The results obtained on using the method proposed in this study were comparable to those obtained with the reference method. The correct classification rates for assigning ignitable liquid residues into ASTM E1618 classes were in the range of 90% for both methods. In comparison to the standard methods HS-MS does have specific advantages. Apart from the speed of the analysis and the fact that the sample does not require sample pre-concentration, this technique is also safer and ecofriendly since it does not use any solvents or produce any residues.

Classification of Weathered Kerosene and Diesel Fuel using Passive Headspace Concentration with Activated Charcoal Strip and Statistical Analysis Technique

Ignitable liquids are present in trace amounts in samples collected from arson scenes therefore their chemical composition often differs from their original composition. This is due to partial evaporation, burning and contamination by pyrolysis products at the scenes. The research was done using two techniques, passive headspace concentration with activated charcoal strip and statistical Analysis, to classify weathered kerosene and diesel fuel. The passive headspace used GC-FID chromatogram pattern to visually identify both weathered ignitable liquids while statistical analysis used cluster formation to group them based on unique characteristics of their hydrocarbons and materials used in the samples. Four case studies were done which consisted of forty-two experiments carried out on twenty-six weathered and unweathered samples that were analyzed under various conditions which included various time of burning, weathering and oven temperature. The Petroleum based ignitable liquids, kerosene and diesel, were used on different types of materials for analysis under various atmospheric conditions. The result showed visual distinction between weathered kerosene and diesel fuel at the initial stage of weathering but it was more difficult to distinguish as samples became weathered over time. Hence, this is one of the reasons why the chromatogram alone cannot be used to visually distinguish between these weathered samples. Therefore, the combination of the chromatographic pattern and statistical method were applied in this research. It was possible to distinguish between the weathered kerosene and diesel fuel using statistical analysis based on n-alkane data derived from Gas Chromatography- Flame Ionization Detector (GC-FID) method.

Application of an HS–MS for the detection of ignitable liquids from fire debris

In arson attacks, accelerants such as ignitable liquids are commonly used to initiate or accelerate a fire. The detection of ignitable liquid residues at fire scenes is therefore a key step in fire investigations. The most widely used analytical technique for the analysis of accelerants is GC–MS. However, pre-concentration of the ignitable liquid residues is required prior to the chromatographic analysis. The standard method, ASTM E1412, involves passive headspace concentration with activated charcoal strips as a method to isolate the ignitable liquid residues from fire debris and these residues are subsequently desorbed from the carbon strip with solvents such as carbon disulfide.In the work described here, an alternative analytical technique based on an HS–MS (headspace mass spectrometry) has been developed for the thermal desorption of the carbon strips and analysis of different ignitable liquid residues in fire debris. The working conditions for the HS–MS analytical procedure were optimized using different types of fire debris (pine wood burned with gasoline and diesel). The optimized variables were desorption temperature and desorption time. The optimal conditions were 145°C and 15min.The optimized method was applied to a set of fire debris samples. In order to simulate post burn samples several accelerants (gasoline, diesel, citronella, kerosene, paraffin, and alcohol) were used to ignite different substrates (wood, cotton, cork, paper, and paperboard). chemometric methods (cluster analysis and discriminant analysis) were applied to the total ion spectrum obtained from the MS (45–200m/z) to discriminate between the burned samples according to the accelerant used. The method was validated by analyzing all samples by GC–MS according to the standard methods ASTM E1412 and ASTM E1618. The results obtained on using the method developed in this study were comparable to those obtained with the reference method. However, the newly developed HS–MS method is faster, safer, and more environmental friendly than the standard method.

Recovery of oxygenated ignitable liquids by zeolites, Part I: Novel extraction methodology in fire debris analysis

The recovery of low molecular weight oxygenates in fire debris samples is severely compromised by the use of heated passive headspace concentration with an activated charcoal strip, as outlined in ASTM E-1412. The term “oxygenate” is defined herein as a small, polar, organic molecule, such as acetone, methanol, ethanol, or isopropanol, which can be employed as an ignitable liquid and referred to in the ASTM classification scheme as the “oxygenated solvents” class. Although a well accepted technique, the higher affinity of activated carbon strips for heavy molecular weight products over low molecular weight products and hydrocarbons over oxygenated products, it does not allow for efficient recovery of oxygenates such as low molecular weight alcohols and acetone. The objective of this study was to develop and evaluate a novel method for the enhanced recovery of oxygenates from fire debris samples. By optimizing conditions of the heated passive headspace technique, the utilization of zeolites allowed for the successful collection and concentration of oxygenates. The results demonstrated that zeolites increased the recovery of oxygenates by at least 1.5-fold compared to the activated carbon strip and may complement the currently used extraction technique.

Microbial degradation of ignitable liquids on building materials

Gasoline was added to moldy samples of unused building materials. The unused samples were allowed to sit at room temperature for 2, 4, 7, and 14 days. Each set of samples was extracted using passive headspace concentration and analyzed using gas chromatography–mass spectrometry. Microbial degradation of the gasoline pattern was observed in limited samples to an extent that could result in an inability to identify an ignitable liquid according to ASTM E1618. The degradation noted was largely consistent with the results of previous microbial studies involving soil.

The Effect of Microbial Degradation on the Chromatographic Profiles of Tiki Torch Fuel, Lamp Oil, and Turpentine*,†

Biodegradation can result in selective removal of many of the compounds required for the identification of an ignitable liquid. In this study, the effects of microbial degradation on tiki torch fuel, lamp oil, and turpentine are reported. Samples of soil spiked with 20 μL of the liquids were stored at room temperature for up to 7 days. The ignitable liquids were then recovered using passive headspace concentration onto charcoal strips followed by solvent elution using pentane. Microbial degradation of tiki torch fuel resulted in the loss of the n-alkanes relative to the branched alkanes. Changes in the profile of the lamp oil were minor due to the highly branched nature of its alkanes. Microbial degradation of turpentine resulted in the selective loss of limonene and o-cymene. Overall, significant degradation by microbial action could result in the inability to identify the presence of an ignitable liquid or misclassify the ignitable liquid found.

Practical Aspects of Analyzing Vegetable Oils in Fire Debris*

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.

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.

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.

The Identification of Isopar H in Vinyl Flooring

Vinyl flooring manufacturers use plasticizers to decrease the viscosity and increase the pliability of vinyl. Several ignitable liquid plasticizers used in the manufacture of vinyl flooring were identified and investigated in this study. Twenty-nine collections from five major vinyl manufacturers, a total of 72 samples, were analyzed using passive headspace concentration in accordance with the American Society for Testing and Materials (ASTM E 1412-00) and gas chromatographic-mass spectrometric (GC-MS) analysis as described in ASTM E 1618-01 (1,2). Norpar products and TXIB (2,2,4-trimethyl-1,3-pentanediol diisobutyrate) are ignitable liquids common to the manufacture of vinyl flooring and were identified in all recently obtained samples. Isopar H is an ignitable liquid found in various products such as charcoal starters, copier toners, and some solvents (2). Of the 29 collections analyzed, Isopar H was only identified in Armstrong's Interflex-Traditions pattern.

Persistence of Floor Coating Solvents

Using passive headspace concentration as described in ASTM E 1412 and gas chromatographic/mass spectrometric (GC/MS) analysis as described in ASTM E 1618, the author has studied the persistence of solvents in floor coating materials. Both oak and pine flooring boards were tested using stain, stain with polyurethane varnish, and oil finish after a period of ten months and 24 months. The solvents from all three floor-coating substances were easily detectable after 24 months, and showed no signs of diminution when compared with the samples tested earlier. These results point out the need for the submission of comparison samples whenever wood flooring samples are submitted for fire debris analysis in suspected arson cases.

The Petroleum-Laced Background

Using passive headspace concentration (ASTM E-1412) and gas chromatographic/mass spectrometric (GC/MS) analysis as described in ASTM E-1618, the authors have studied the volatile components detectable in several kinds of otherwise uncontaminated substrata, including clothing, shoes, household products, building materials, paper products, cardboard, and adhesives. Due to the use of petroleum-derived liquids in the manufacture of these materials, it is frequently possible to detect the liquids, even when the products are several years old. These results point out the need for the use of comparison samples whenever possible.