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The sampling of ignitable liquids on suspects’ hands
Forensic Science International 194 (2010) 115–124
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Forensic Science International journal homepage: www.elsevier.com/locate/forsciint
The sampling of ignitable liquids on suspects’ hands Isabelle Montani *, Ste´fane Comment, Olivier Dele´mont Institut de Police Scientifique, Ecole des Sciences Criminelles, Universite´ de Lausanne, Batochime, CH-1015 Lausanne-Dorigny, Switzerland
A R T I C L E I N F O
A B S T R A C T
Article history: Received 12 March 2009 Received in revised form 14 October 2009 Accepted 19 October 2009 Available online 2 December 2009
In arson cases, the collection and detection of traces of ignitable liquids on a suspect’s hands can provide information to a forensic investigation. Police forces currently lack a simple, robust, efficient and reliable solution to perform this type of swabbing. In this article, we describe a study undertaken to develop a procedure for the collection of ignitable liquid residues on the hands of arson suspects. Sixteen different collection supports were considered and their applicability for the collection of gasoline traces present on hands and their subsequent analysis in a laboratory was evaluated. Background contamination, consisting of volatiles emanating from the collection supports, and collection efficiencies of the different sampling materials were assessed by passive headspace extraction with an activated charcoal strip (DFLEX device) followed by gas chromatography–mass spectrometry (GC–MS) analysis. After statistical treatment of the results, nonpowdered latex gloves were retained as the most suitable method of sampling. On the basis of the obtained results, a prototype sampling kit was designed and tested. This kit is made of a three compartment multilayer bag enclosed in a sealed metal can and containing three pairs of non-powdered latex gloves: one to be worn by the sampler, one consisting of a blank sample and the last one to be worn by the person suspected to have been in contact with ignitable liquids. The design of the kit was developed to be efficient in preventing external and cross-contaminations. ß 2009 Elsevier Ireland Ltd. All rights reserved.
Keywords: Arson Flammable liquid Gasoline Swab Gloves Transfer Hands
1. Introduction When a fire is deliberately started, arsonists sometimes use ignitable liquids that they pour on the site to help ignite and propagate the fire and thus accelerate destruction. The detection and analysis of these ignitable liquid residues are routinely carried out in order to determine which type of liquid accelerant was used, thus giving investigators important information that can be useful in explaining the cause and propagation of the fire, gaining intelligence on a series of offenses, and even pointing to or excluding suspects [1,2]. It is often difficult to prove that an arson suspect is at the origin of a criminal fire, since evidence that could be used to identify him, such as DNA or fingerprints, is often destroyed or not even searched for [3]. Other physical evidence can be looked for on the suspect, such as burn marks on skin and/or clothes, or in his/her surroundings, such as ignition equipment. Unfortunately, these types of traces do not allow the investigator to link the suspect directly to the crime scene. These observations led to the necessity of developing an effective and simple method for the collection of ignitable liquids
* Corresponding author. Tel.: +41 21 692 46 47; fax: +41 21 692 46 05. E-mail address: [email protected] (I. Montani). 0379-0738/$ – see front matter ß 2009 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.forsciint.2009.10.024
on hands. Indeed, it is widely acknowledged that gasoline, when deliberately poured on the ground or on furniture, can splatter onto the arsonist’s shoes, clothing and hands [15,16]. A study conducted by Coulson and Morgan-Smith [4] showed that, after 2 l of gasoline were poured onto the floor, considerable amounts could be recovered on shoes and clothing (up to 30 ml). The detection of these ignitable liquids on suspects could be used as trace evidence in a judicial perspective or as piece of intelligence in a police enquiry. Thus, the development of a technique capable of transferring these traces present on the suspect’s hands onto a material, which could then be exploited in the crime laboratory, could prove to be very useful. This swabbing technique could be integrated into a kit. Indeed, the need for a kit which could be used on the spot is very important, considering the degradation and rapid evaporation of gasoline on hands [5]. The development of complete and ready-to-use swabbing kits is thus very important in regard to the problems listed above. A review of the existing literature revealed that little research has been published on the topic. One of the most recent, presented by Darrer et al. [5], was used as a basis for this research. In this study, four types of methods for collecting gasoline on hands were tested: polyethylene gloves, latex gloves, polyvinyl gloves and humidified cotton swabs. Tests of the supports’ background noise, as well as tests on their efficiency in the collection of gasoline, were conducted. The authors found that powdered polyvinyl gloves
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116 Table 1 Collection supports studied. Support composition
Company
Brand
VWRTM International VWRTM International Sempercare1 Sempercare1 edition Qualimed1 Ansell Medical Sempermed1 supreme
Latex
Semperguard1 Semperguard1 Maxxim Medical Europe
Polyvinyl
P NP P NP P P NP
Gammex1
Semperguard1 Semperguard1 Ansell Ansell
Nitrile
Powdered (P)/ non-powdered (NP)
TT1Clear
P NP P
Synthetic elastomer
Biogel SkinsenseTM N
Regent1
NP
Swabsa
Johnson & Johnson Medical
TopperTM 12
–
a
1
Touch N Tuff1 Touch N Tuff1
P NP P NP
Each package contained two 5 by 5 cm sterile swabs. The swabs were impregnated with pentane during the experiments.
presented the least background noise and had the best efficiency in the collection of gasoline. Rolph [6] conducted the same type of study on five supports: nitrile, vinyl and cotton gloves, as well as cotton balls and cotton gloves under nitrile gloves. These supports were examined in terms of background interference and gasoline collection efficiency. Her research showed that the nitrile gloves were the most efficient in retaining fresh gasoline. The vinyl gloves produced good results; however they had high amounts of background interference. The other types of supports were shown to be ineffective in the collection and detection of gasoline on hands. On the basis of these two researches, a study was undertaken in order to analyze a much larger sample of collection supports using more sensitive analytical techniques. This is carried out in order to determine which support would best suit the set goals. The present study had two objectives. The first was to determine which procedure was the most effective in collecting and detecting the gasoline present on a person’s hands. The second was to elaborate a kit for sampling gasoline on arson suspects’ hands. 2. Materials and methods 2.1. Materials The three glove compositions most widely available on the market were selected; latex, nitrile and polyvinyl gloves were chosen, both in the powdered and the non-powdered versions. Gloves made of another synthetic elastomer and cotton swabs were also tested, resulting in a total of 16 different supports. Table 1 gives an overview of the different supports analyzed. The ignitable liquid used throughout the study was unleaded, regular-grade gasoline purchased from a local gas station. The chemicals used throughout the study (i.e., carbon disulfide for the desorption of the strips, 2-hexanone as the internal standard (IS), pentane and dichloromethane) were obtained from Fluka. 2.2. Instrumentation All of the obtained samples were analyzed with an Agilent Technologies 6890N gas chromatograph, coupled with an Agilent Technologies 5975 inert mass spectrometer. The following parameters were selected: Column: HP-5MS,
30 m 0.25 mm i.d. with 0.25 mm film thickness; carrier gas: helium at 1 ml/ min constant flow; inlet temperature: 250 8C; volume injection: 1 ml with 1:25 split ratio; oven program: 50 8C isotherm for 3 min, 5 8C/min up to 250 8C and 250 8C isotherm for 20 min; mass spectrometer ionization source at 230 8C; mass quadrupole analyzer at 150 8C in scan mode (m/z 10–450) with a sampling rate of 1.7 scan s 1. The robustness and repeatability of this method was monitored by periodic injections of a standard mixture of Restek E1618 Test Mix diluted in CH2Cl2 with a concentration of 0.005% (v/v) for each compound. Injections were performed during the whole duration of the study: once before the beginning of the study and once a week throughout the study. The RSD values obtained, indicated in Table 2, assess the robustness and repeatability of the method. The gas chromatography–mass spectrometry (GC–MS) apparatus was piloted with the Agilent MSD Chemstation (version D.02.00.275). The chromatograms and the mass spectra were visualized with the same software. Solvent controls were run before each analysis with the same solvent used for the analysis (CS2 or CS2 with 0.5% (v/v) 2-hexanone (IS)) to ensure that the solvent, the injection syringe, the injector and the column were not contaminated.
3. Experiment 3.1. Gasoline identification criteria The identification of gasoline throughout the whole study was carried out in agreement with the criteria recommended by the American Society for Testing and Materials (ASTM) E 161806 [7]. This standard states that the 4-peak group of C3alkylbenzenes [1-ethyl-3-methylbenzene and 1-ethyl-4-methylbenzene, 1,3,5-trimethylbenzene, 1-ethyl-2-methylbenzene, 1,2,4-trimethylbenzene] must be present, because it is found in 90% evaporated gasoline. Lighter components, namely the group of C2-alkylbenzenes (ethylbenzene and xylenes), were added as requirements for identification since the gasoline used in the experiments was ‘‘fresh’’, thus practically unevaporated. Moreover, two C4-alkylbenzenes were also considered: 1,2,4,5tetramethylbenzene and 1,2,3,5-tetramethylbenzene. In order to note the presence of gasoline, it was necessary for all the gasoline components cited to be present in the extracted ion chromatograms (EIC). Table 3 shows the target components of gasoline considered during this study.
Table 2 Percent relative standard deviations (RSD%) of peak areas for compounds of the standard Restek E1618 Test Mix calculated for five injections performed through the whole duration of the study. Compound
Toluene
p-Xylene
1-Ethyl-2-methyl-benzene
1-Ethyl-3-methyl-benzene
1,2,4-Trimethyl-benzene
C10
C12
C14
C16
RSD% [n = 5]
5.72
3.30
2.91
3.00
3.33
2.64
4.29
4.81
5.39
I. Montani et al. / Forensic Science International 194 (2010) 115–124 Table 3 Target compounds of gasoline. C2-alkylbenzenes
Ethylbenzene m-, p-Xylenea o-Xylene
C3-alkylbenzenes
Propylbenzene 1-Ethyl-3-methylbenzene and 1-ethyl-4-methylbenzenea 1,3,5-Trimethylbenzene 1-Ethyl-2-methylbenzene 1,2,4-Trimethylbenzene 1,2,3-Trimethylbenzene
C4-alkylbenzenes a
1,2,4,5-Tetramethylbenzene 1,2,3,5-Tetramethylbenzene
Unresolved peaks.
3.2. Establishment of calibration curves for the analytical method A calibration of the GC–MS method was undertaken in order to control and assess the linearity of the response of the detector for the analysis of the target compounds of gasoline presented in Table 3. For that, several known gasoline concentrations, combined with a fixed volume of internal standard, were injected (three times each) and analyzed in the same conditions as those employed during the experiments. The concentrations were selected in order to cover the whole range of concentrations likely to intervene later on during the tests, as suggested by Miller and Miller [8]. The coefficients of correlation (R) of all of the target compounds were significant after the application of the T-test (95%), done both before and after the calibration of the mass spectrometer (tune). However, a small improvement concerning the coefficient of regression was observed during the second analysis. 3.3. Evaluation of the background of the collection supports This first part of the project, concerning the choice of the supports, consisted in studying the volatile compounds the different collection supports might release. Indeed, some of the sample matrices may produce interfering volatiles, which could hinder subsequent identification process of ignitable liquid traces [9]. For that matter, the vapors produced by the tested supports during the heating process were studied using the technique of passive adsorption. The background noise generated by each support as well as its risk of interference with the profile of ignitable liquids (mainly gasoline) was evaluated by considering total ions chromatograms (TIC) and extracted ion chromatograms (EIC) for aromatic hydrocarbons (ions 91, 105, 106, 119, 120 and 134), alkanes (ions 57, 71 and 85) and alkenes (ions 55 and 69). The collection supports to be tested (a pair of gloves or the swabs) was placed in a nylon-11 type bag (obtained from BVDA, NL). A 1 dm3 frame (in the shape of a truncated cone) made of copper wire was also added inside of each bag, in order to maintain a reproducible analysis volume. An activated charcoal strip, part of a DFLEX device (obtained from Albrayco Laboratories Inc., USA), was hung above the sample. The bag was sealed with a tight knot, then heated in an oven at 60 8C during 16 h, using the technique of passive headspace concentration [10–12]. Finally, the activated charcoal strip was desorbed with 800 ml of carbon disulfide (CS2) and the solution was analyzed by GC–MS. Three pairs of each of the 16 collection supports were tested following this procedure, resulting in a total of 48 analyses. Blanks of the nylon-11 bags were analyzed in between each sample to ensure that the ovens were not contaminated. Only the supports that gave the best results in terms of background noise, in other words, the ones with the least
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interfering volatiles, were kept for the second part of the study, where their efficiency in terms of collection of gasoline could be evaluated. 3.4. Efficiency of gasoline collection In this stage, the efficiency of the gloves and the swabs as means to collect gasoline on hands was tested. The adopted procedure was devised as to avoid as much contamination as possible (use of sterilized tools, no contact between the tester and the subjects, etc.). The four supports that were selected after the evaluation of background volatiles were studied under two perspectives. The first angle was to test their reproducibility concerning the collection of gasoline, when tested on a same person. This made it possible to evaluate the variations due to the method, the conditioning of the sample and the analysis which followed, while minimizing the influence due to the subject’s skin. Each support was tested three times on a same subject, totaling up to 12 analyses. In the second stage, each support was tested four times, each time on a different person. This made it possible to evaluate the variation of the capacity of collection of each support. The variation is due to the different types of skin of the subjects, their level of perspiration and other uncontrollable variables. For both experiments, 50 ml of gasoline was deposited using a micro-syringe (PerkinElmer, 50) in the right palm of the subject who proceeded to briefly rub his hands together. This was not carried out in a fumehood in order to avoid an unrealistic accelerated vaporization of the gasoline compounds. The subjects had not been in contact with any ignitable liquids in the last 48 h. Indeed, Darrer et al. [5] showed that after 120 min, the 500 ml of gasoline deposited on a person’s hand could not be detected according to the ASTM standards. The subject put on the gloves to be tested (which were deposited beforehand on a clean surface) and wore them for 20 min in a temperate room, following the conditions recommended by Darrer et al. [5]. The gloves were then placed in a nylon11 bag containing the metal frame of 1 dm3. An activated charcoal strip was added and the bag was sealed with a tight knot. The bag was then heated in an oven at 60 8C during 16 h, using the technique of passive headspace concentration. Finally, the activated charcoal strip was desorbed with 800 ml of carbon disulfide (CS2) with 0.5% (v/v) of 2-hexanone as internal standard. The eluate was analyzed by GC–MS. For the sampling with the swabs, 3 ml of pentane were dispersed on each one of the two swabs, which was then immediately rubbed on the palm, the fingers, the back of the hand and finally between the fingers. This was done until the pentane had completely evaporated (which corresponds to approximately 30–60 s). The operation was repeated on the other hand with the second swab. The swabs were then conditioned and sampled in the same way as the gloves. Each collection support was tested four times, each time on a different volunteer, giving a total of 16 analyses. 4. Results 4.1. Evaluation of the background of the collection supports The three chromatograms obtained for each type of gloves or swabs were examined. The compounds of gasoline, as well as the principal compounds of the other hydrocarbon classes described above, were searched for in each total ions chromatogram and its extracted ion chromatogram. The chromatogram obtained after the analysis of the nylon-11 bag blank gave the following peaks, in
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order of elution: acetone, carbon disulfide (CS2), benzene (all due to the solvent), followed by methylisobutylcetone (MIK), toluene and the limonene (all due to the nylon-11 bags). Given the presence of toluene, due to an external and non-controllable factor (the nylon-11 bags), this compound was not considered as a target compound during the study. Clearly, to take it into account would distort the interpretation of the results. The study of chromatograms of the background noise generated by the 16 supports tested allowed the following observations to be formulated: for each type of glove, the three analyzed pairs present qualitatively similar results with some small variations concerning the intensity of the peaks. The latex gloves gave in general much better results than the other types of gloves, which often presented series of alkanes. These alkanes are problematic because they interfere with a general search of hydrocarbons, since they are components of flammable substances of the ‘‘Heavy’’ class (such as kerosene and diesel). A quick overview of the main components observed for each type of tested support is presented in Table 4: In light of these results, the following gloves were retained for the subsequent part of the study: both of the VWRTM International latex gloves, in the powdered and non-powdered version, as well as the Sempercare1 edition latex gloves (non-powdered). All of the vinyl and nitrile gloves, as well as the gloves made of synthetic elastomer, were eliminated because of their strong production of volatile compounds interfering with the detection of small amounts of gasoline or other hydrocarbon classes such as the heavy petroleum distillates (kerosene, diesel, etc.). The TopperTM 12 medical swabs were also retained given that no volatiles were detected. Figs. 1–3 present the background noise of the non-powdered and powdered VWRTM International latex gloves and Sempercare1
edition latex gloves (non-powdered). Fig. 4 presents the background noise of the TopperTM 12 medical swabs and Fig. 5 the strong volatile profile obtained with the Semperguard1 nitrile gloves (non-powdered). 4.2. Collection efficiency of the retained supports In the first stage, the reproducibility of the developed method was tested with a deposition of 50 ml of gasoline, always on the hands of the same person, three times per each collection mean. This allowed the intravariability generated by each type of support to be evaluated by reducing as much as possible the parameters that could have an influence on the collection efficiency of the gloves (type of skin, perspiration, etc.). The area of each compound of interest on the area of the internal standard was calculated, giving a ratio (normalization). The results obtained appear in Fig. 6 (mean values and standard deviation) and Table 5 (relative standard deviation). Except for the TopperTM 12 swabs that also collected very few volatiles, an acceptable variation was observed for all the tested supports, showing that the reproducibility of the method was satisfactory. Once the reproducibility of the method was established, the efficiency of collection of each type of support could be evaluated. For each collection support, four samples were obtained with four different subjects and an initial amount of 50 ml of gasoline. The ratio of the area of each compound of interest, normalized to the internal standard was calculated in the same manner as above. Thus, the intervariability of the effectiveness of collection was estimated. The averages of the ratios of areas obtained, as well as the standard deviation calculated for each support, are presented below in Fig. 7.
Table 4 Main volatile compounds detected in the different studied collection supports. Collection support tested (brand) Latex
Powdered (P)/nonpowdered (NP)
Main volatile compounds detected
VWRTM International
P
VWRTM International Sempercare1
NP P
Sempercare1 edition
NP
Aromatics components of the C2 and C3 groups, as well a-pinene were present in trace in the Extracted Ion Mode N-alkanes from C10 to C14 were also present in very small quantities Both gloves presented chromatograms similar to those of VWRTM International, but with the a-pinene peak of strong intensity The powdered version presented, in addition, a strong peak of an aromatic derivative between C10 and C11 Presence of several peaks of strong intensity in the C10 to C14 range The chromatograms obtained showed several alkane peaks of great intensity in the C10 to C13 range (in a Gaussian distribution) C2 and C3 aromatic groups and a-pinene were present The chromatograms obtained were similar to the VWRTM International, with, in addition, the presence of a-pinene and a aromatic derivate between C10 and C11
Qualimed
Nitrile
Polyvinyl
1
P
Ansell Medical Gammex1
P
Sempermed1 supreme
NP
Semperguard1
P
Semperguard1 Ansell Touch N Tuff1
NP P
Ansell Touch N Tuff1
NP
Semperguard
1
P
C11 to C16 in the distinctive Gaussian distribution Alkane interferences and olefinic hydrocarbons were present in a significant number The powdered version had a series of aromatics between C15 and C19 The chromatograms obtained were very similar to the one obtained with the non-powdered Semperguard1 gloves
Strong presence of the C10 to C18 n-alkanes in a distinctive Gaussian distribution, characteristic of heavy petroleum distillates (kerosene, diesel) C2, C3 and C4-alkylbenzenes groups were slightly present. The chromatograms obtained were similar to the Semperguard gloves, with, in addition, a large amount of aromatic compounds between C10 and C15
Semperguard1 Maxxim Medical Europe TT1Clear
NP P
Synthetic elastomer
Biogel1 SkinsenseTM N Regent1
NP
Very badly defined base line due to the presence of alkanes and olefinic hydrocarbons Various aromatic compounds were present, but in small quantities.
Swabs
Johnson & Johnson Medical TopperTM 12
–
No volatiles detected
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Fig. 1. Chromatogram of the background noise of the non-powdered VWRTM International latex gloves with abundance scaled at 2 104; the full-scale chromatogram is presented in inclusion. The peaks marked with the asterisk glyph arise from the sampling bag and from the elution solvent.
Fig. 2. Chromatogram of the background noise of the powdered VWRTM International latex gloves with abundance scaled at 2 104; the full-scale chromatogram is presented in inclusion. The peaks marked with the asterisk glyph arise from the sampling bag and from the elution solvent.
On average, the non-powdered VWRTM International latex gloves gave the best results (Fig. 8), followed by the powdered VWRTM International gloves (Fig. 9), the non-powdered Sempercare1 gloves, then finally the TopperTM 12 swabs.
In order to evaluate the variations observed in the results, a statistical comparison was carried out with the software SPSS1 12.0. Multivariate analyses of the variance (Manova) were carried out on the ratios of the areas of all the gasoline compounds of each
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Fig. 3. Chromatogram of the background noise of the non-powdered Sempercare1 edition latex gloves with abundance scaled at 2 104; the full-scale chromatogram is presented in inclusion. The peaks marked with the asterisk glyph arise from the sampling bag and from the elution solvent.
support, to determine if a significant difference could be assessed between the different supports tested [13]. Although the nonpowdered VWRTM International gloves are on average almost twice more effective than the other supports tested, they
presented, with a confidence interval of 95%, no statistical difference with the other types of gloves. In fact, only the swabs were significantly less effective in the collection of the gasoline, compared to the powdered and the non-powdered VWRTM
Fig. 4. Chromatogram of the background noise of the TopperTM 12 medical swabs with abundance scaled at 2 104; the full-scale chromatogram is presented in inclusion. The peaks marked with the asterisk glyph arise from the sampling bag and from the elution solvent.
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Fig. 5. Chromatogram of the background noise of the Semperguard1 nitrile gloves (non-powdered) with abundance scaled at 1 106; the full-scale chromatogram is presented in inclusion. The peaks marked with the asterisk glyph arise from the sampling bag and from the elution solvent.
Fig. 6. Reproducibility of the method: for each collection support, three samples were collected from the same person. The figure depicts the mean values and standard deviations of the ratio of the target peak area to the internal standard area for each of the target gasoline compounds.
International latex gloves. No other statistically significant difference was observed. The small differences observed between the tested gloves could be due to differences they present in hydrocarbon permeability or in their capacity to make the skin perspire. The presence of talcum powder in some of the gloves could create a concurrent site for vapor adsorption and thus influence the amount of volatiles extracted by the passive headspace method. The important difference observed between the gloves and the swabs could be due to differences between the two collection processes such as the application time. Indeed, the gloves remained on the individual’s hands for 20 min,
whereas the swabs were applied less than 1 min on each hand, until the pentane had completely evaporated. In light of the results obtained on the interferences of the volatile products generated by the collection support, as well as the evaluation of their capacity and efficiency to collect gasoline, the non-powdered VWRTM International latex gloves were selected. In the optic of a swabbing kit, these gloves are recommended so far for collecting ignitable liquids on a person’s hands. As for the swabs, even though they generated no interferences, they were not retained on the basis of their low collection efficiency of gasoline during the tests.
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Table 5 Percent relative standard deviations (RSD%) of the normalized peaks of the target gasoline compounds for each collection mean. RSD% [n = 3]
Ethylbenzene p-, m-Xylene o-Xylene Propylbenzene 1-Ethyl-3(4)methylbenzene 1,3,5-Trimethylbenzene 1-Ethyl-2-methylbenzene 1,2,4-Trimethylbenzene 1,2,3-Trimethylbenzene 1,2,4,5-Tetramethylbenzene 1,2,3,5-Tetramethylbenzene
Non-powdered VWR International latex gloves
Powdered VWR International latex gloves
Non-powdered Sempercare latex gloves
Topper 12 Medical swabs
17.66 22.12 22.52 33.44 34.55 34.39 33.69 33.68 29.54 27.37 23.40
10.64 10.18 10.02 7.57 7.27 8.81 9.31 7.70 9.92 7.66 7.44
25.03 24.07 28.63 26.22 27.77 28.38 29.46 27.83 28.23 27.85 27.44
44.04 43.34 55.35 42.36 56.02 56.88 62.36 64.83 69.90 68.68 76.44
4.3. Development of a sampling kit Once the optimal support was chosen, a sampling kit for use on people suspected of illegal involvement with ignitable liquids was developed. The authors were inspired by the study conducted by Wallace and McKeown, who developed sampling procedures for firearms and explosives residues [14]. The kit had several objectives: it had to be compact and practical, present an ease of use and preparation, and, most importantly, it had to be the least susceptible to any exterior contamination. The collection supports had to have the best collection efficiency and the least background noise possible. With these elements in mind, a prototype suspect sampling kit was designed and tested successfully. The kit is contained in a multilayer DUO-GASBAGS bag (obtained from KTM-Krim Teknisk Materiel AB, Sweden) that is divided into three parts with the help of a thermal sealer. The separation into three compartments minimizes the risk of cross-contaminations between each section. The first section of the kit contains a first pair of VWRTM International non-powdered gloves to be worn by the sampler, along with comprehensive instructions. The second part contains a pair of VWRTM International non-powdered gloves that consists of the blank sample, a nylon-11 bag, a technical form to be filled out by the sampler and a paperclip. These gloves are to be placed in the sampling area, while the sampling of the suspect is carried out, and thus provide a control sample of both the sampling environment as well as of the conditioning and storage of the kit. The third section of the kit contains the sampling material, i.e.
a second pair of VWRTM International non-powdered gloves, a nylon-11 bag, a technical form and a paperclip. This pair of gloves is the closest possible to the blank gloves in terms of origin (they are taken from the same lot) and storage conditions, to ensure optimal control conditions. The kit can finally be integrated in a metal paint can, closed hermetically and sealed with an instructive label. The use of a metal can makes it possible to overcome a great disadvantage associated with the use of a multilayered bag only: the storage of the kits in places that can present contaminations, such as, for example, in cars. Indeed, the metal boxes present an additional impermeability to those of the bags alone, as well as a mechanical barrier to perforations that bags can be subject to. 4.4. Using the kit Before opening the kit, several precautions should be observed by the sampler: they can be stated on the outer label. Their purpose is to minimize any contamination that could occur during the sampling and conditioning phase, such as sampling in an environment contaminated with a ignitable liquid. The sampler proceeds by opening the metal can, and taking out the multilayer bag. He/she opens it on the designated side, puts on his/her pair of gloves, then takes out the control sample gloves and puts them in the nylon-11 bag. This bag is left open during the whole swabbing process and is latterly sealed. The sampler then gives the sampling gloves to the suspect, who proceeds to put them on himself/herself and wears them for
Fig. 7. Efficiency of collection: a group of four persons was considered. For each collection support, one sample was collected on each member of the group, giving a total of four samples per support. The figure depicts the mean values and standard deviations of the ratio of the target peak area to the internal standard area for each of the target gasoline compounds.
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Fig. 8. Chromatogram of one collection test undertaken with the non-powdered VWRTM International latex gloves with abundance scaled at 7 104. The peaks marked with the asterisk glyph arise from the sampling bag and from the elution solvent; two other peaks (IS) arise from the internal standard added to the elution solvent.
Fig. 9. Chromatogram of one collection test undertaken with the powdered VWRTM International latex gloves with abundance scaled at 7 104. The peaks marked with the asterisk glyph arise from the sampling bag and from the elution solvent; two other peaks (IS) arise from the internal standard added to the elution solvent.
20 min. The suspect then takes off his gloves himself by unrolling them and places them in the nylon-11 bag. The sampler then seals the bag by making a double knot and annexes
the form to the bag. Both samples (the control and the suspect sample) are to be transmitted to a laboratory as quickly as possible for analysis or to be stored in a refrigerator, avoiding
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contact between both samples. It is also suggested to remove the suspect’s clothes and shoes for a complementary ignitable liquid analysis, as recommended by Coulson and Morgan-Smith [4]. 5. Discussion During the study of the intravariability of the gasoline collection from the tested supports, small differences were recorded. They could be due to several factors, such as the conditions under which the swabbing took place (primarily the temperature), losses that occurred during the adsorption and desorption of the compounds on the activated charcoal strip. The study of the efficiency of collection made it possible to note that, except for the Sempercare1 edition gloves, the gasoline collection efficiency of the supports on different people (intervariability) presented a greater variation than the results obtained for the collection on a same person (intravariability). These differences are primarily due to the factors referred to above, as well as other external factors, such as differences in the types of skin and perspiration of the subjects. The non-powdered VWRTM International latex gloves had the best results in terms of gasoline collection at the time t = 0. The possibility that another type of support would be more effective than the latex gloves after a certain amount of time cannot be ruled out. Indeed, the pentane-soaked swabs could be more suited to the collection of the gasoline after a certain amount of time has passed, pentane presenting a better affinity with the heavier compounds. Moreover, the compress could be employed in sequence after the gloves are worn. This method is all the more interesting since suspected arsonists are seldom stopped immediately after having committed the crime. A certain amount of time has already elapsed. On the other hand, it could be more convincing, from an interpretative point of view, to find light compounds, since their persistence is less than that of heavier compounds. The developed sampling kit also has the advantage of providing the sampler with a blank swab. This blank originates from the same pack as the gloves used for swabbing the suspect and is handled and stored under the same conditions as the latter. The blank also allows the swabber to obtain a blank of the environment in which the swabbing takes place. 6. Conclusion This research was directed toward the study of collection of ignitable liquids on arson suspects’ hands, implying the use of accelerants. The purpose of this work was to determine the best method for collecting and detecting gasoline on a suspect’s hands and to advise the development of a simple and effective sampling kit. Sixteen swab collection supports were evaluated, on the criteria of their background noise and their effectiveness in the collection of gasoline. The volatiles that emanated from the collection supports were analyzed by GC–MS after a passive headspace extraction procedure. Only four collection supports offered acceptable levels of background contamination: three types of
latex gloves and sterile medical swabs. These four collection supports were then tested to see which was the most effective in the collection of gasoline on hands. Although the non-powdered VWRTM International latex gloves were not statistically better than the other types of supports tested, they showed the best average during the tests and were therefore selected for the sampling of ignitable liquids on hands. This information allowed the authors to develop a prototype of a simple and effective kit for the sampling of ignitable liquids on arson suspects’ hands. The main goals set before the establishment of the kit were respected. The developed kit is easy to use, practical, compact and in terms of storage and all precautions were taken in order to minimize external contaminations due to storage, transport and manipulation. Acknowledgement We acknowledge Mr Eric Stauffer whose comments greatly improved this manuscript. References [1] W. Bertsch, G. Holzer, C. Sellers, Chemical Analysis for the Arson Investigator and Attorney, Huethig Buch Verlag, 1993. [2] E. Stauffer, J.A. Dolan, R. Newman, Fire Debris Analysis, Academic Press, 2007. [3] J.D. DeHaan, Kirk’s Fire Investigation, 5th ed., Prentice Hall, Brady, 2002. [4] S.A. Coulson, R.K. Morgan-Smith, The transfer of petrol on to clothing and shoes while pouring petrol around a room, Forensic Science International 112 (2–3) (2000) 135–141. [5] M. Darrer, J. Jacquemet-Papilloud, O. Dele´mont, Gasoline on hands: preliminary study on collection and persistence, Forensic Science International 175 (2–3) (2008) 171–178. [6] E. Rolph, Petrol on Hands: Handling Method and Validity of Results, Department of Chemistry, University of Technology, Sydney, 2000. [7] ASTM, E1618-06: Standard test method for ignitable liquid residues in extracts from fire debris samples by gas chromatography-mass spectrometry 1, Annual ASTM Standards on Disc, vol. 14.02, 2007, American Society for Testing and Materials. [8] J.N. Miller, J.C. Miller, Statistics and Chemometrics for Analytical Chemistry, 5th ed., Pearson Education Limited, Harlow, England, 2005. [9] A.D. Pert, M.G. Baron, J.W. Birkett, Review of analytical techniques for arson residues, Journal of Forensic Sciences 51 (5) (2006) 1033–1049. [10] J.F. Demers-Kohls, S.L. Ouderkirk, J.L. Buckle, W.E. Norman, N.S. Cartright, C. Dagenais, Evaluation of the DFLEX device for fire debris analysis, Journal of the Canadian Society of Forensic Science (1994) 99–123. [11] R.T. Newman, W.R. Dietz, K. Lothridge, The use of activated charcoal strips for fire debris extractions by passive diffusion. Part 1: The effects of time, temperature, strip size, and sample concentration, Journal of Forensic Sciences 41 (3) (1996) 361–370. [12] ASTM, E1412-00: Standard practice for separation of ignitable liquid residues from fire debris samples by passive headspace concentration with activated charcoal, Annual ASTM Standards on Disc, vol. 14.02, 2007, American Society for Testing and Materials. [13] J. Bray, S. Maxwell, Multivariate Analysis of Variance, Sage University Paper Series on Quantitative Research Methods, 1985, p. 54. [14] J. Wallace, W. McKeown, Sampling procedures for firearms and/or explosives residues, Journal of Forensic Science Society 33 (1993) 107–116. [15] F. Terrapon, J. Papilloud, E. Du Pasquier, J. Martin, Persistence of gasoline on jeans, in: First European Meeting of Forensic Science, Lausanne, September 17–19, 1997. [16] T. Folkman, A. Kuehl, R. Groves, A. Beveridge, Evaporation rate of gasoline from shoes, clothing, wood and carpet materials and kerosene from shoes and clothing, Canadian Society Forensic Science Journal 23 (2 & 3) (1990) 49–59.
Contents lists available at ScienceDirect
Forensic Science International journal homepage: www.elsevier.com/locate/forsciint
The sampling of ignitable liquids on suspects’ hands Isabelle Montani *, Ste´fane Comment, Olivier Dele´mont Institut de Police Scientifique, Ecole des Sciences Criminelles, Universite´ de Lausanne, Batochime, CH-1015 Lausanne-Dorigny, Switzerland
A R T I C L E I N F O
A B S T R A C T
Article history: Received 12 March 2009 Received in revised form 14 October 2009 Accepted 19 October 2009 Available online 2 December 2009
In arson cases, the collection and detection of traces of ignitable liquids on a suspect’s hands can provide information to a forensic investigation. Police forces currently lack a simple, robust, efficient and reliable solution to perform this type of swabbing. In this article, we describe a study undertaken to develop a procedure for the collection of ignitable liquid residues on the hands of arson suspects. Sixteen different collection supports were considered and their applicability for the collection of gasoline traces present on hands and their subsequent analysis in a laboratory was evaluated. Background contamination, consisting of volatiles emanating from the collection supports, and collection efficiencies of the different sampling materials were assessed by passive headspace extraction with an activated charcoal strip (DFLEX device) followed by gas chromatography–mass spectrometry (GC–MS) analysis. After statistical treatment of the results, nonpowdered latex gloves were retained as the most suitable method of sampling. On the basis of the obtained results, a prototype sampling kit was designed and tested. This kit is made of a three compartment multilayer bag enclosed in a sealed metal can and containing three pairs of non-powdered latex gloves: one to be worn by the sampler, one consisting of a blank sample and the last one to be worn by the person suspected to have been in contact with ignitable liquids. The design of the kit was developed to be efficient in preventing external and cross-contaminations. ß 2009 Elsevier Ireland Ltd. All rights reserved.
Keywords: Arson Flammable liquid Gasoline Swab Gloves Transfer Hands
1. Introduction When a fire is deliberately started, arsonists sometimes use ignitable liquids that they pour on the site to help ignite and propagate the fire and thus accelerate destruction. The detection and analysis of these ignitable liquid residues are routinely carried out in order to determine which type of liquid accelerant was used, thus giving investigators important information that can be useful in explaining the cause and propagation of the fire, gaining intelligence on a series of offenses, and even pointing to or excluding suspects [1,2]. It is often difficult to prove that an arson suspect is at the origin of a criminal fire, since evidence that could be used to identify him, such as DNA or fingerprints, is often destroyed or not even searched for [3]. Other physical evidence can be looked for on the suspect, such as burn marks on skin and/or clothes, or in his/her surroundings, such as ignition equipment. Unfortunately, these types of traces do not allow the investigator to link the suspect directly to the crime scene. These observations led to the necessity of developing an effective and simple method for the collection of ignitable liquids
* Corresponding author. Tel.: +41 21 692 46 47; fax: +41 21 692 46 05. E-mail address: [email protected] (I. Montani). 0379-0738/$ – see front matter ß 2009 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.forsciint.2009.10.024
on hands. Indeed, it is widely acknowledged that gasoline, when deliberately poured on the ground or on furniture, can splatter onto the arsonist’s shoes, clothing and hands [15,16]. A study conducted by Coulson and Morgan-Smith [4] showed that, after 2 l of gasoline were poured onto the floor, considerable amounts could be recovered on shoes and clothing (up to 30 ml). The detection of these ignitable liquids on suspects could be used as trace evidence in a judicial perspective or as piece of intelligence in a police enquiry. Thus, the development of a technique capable of transferring these traces present on the suspect’s hands onto a material, which could then be exploited in the crime laboratory, could prove to be very useful. This swabbing technique could be integrated into a kit. Indeed, the need for a kit which could be used on the spot is very important, considering the degradation and rapid evaporation of gasoline on hands [5]. The development of complete and ready-to-use swabbing kits is thus very important in regard to the problems listed above. A review of the existing literature revealed that little research has been published on the topic. One of the most recent, presented by Darrer et al. [5], was used as a basis for this research. In this study, four types of methods for collecting gasoline on hands were tested: polyethylene gloves, latex gloves, polyvinyl gloves and humidified cotton swabs. Tests of the supports’ background noise, as well as tests on their efficiency in the collection of gasoline, were conducted. The authors found that powdered polyvinyl gloves
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116 Table 1 Collection supports studied. Support composition
Company
Brand
VWRTM International VWRTM International Sempercare1 Sempercare1 edition Qualimed1 Ansell Medical Sempermed1 supreme
Latex
Semperguard1 Semperguard1 Maxxim Medical Europe
Polyvinyl
P NP P NP P P NP
Gammex1
Semperguard1 Semperguard1 Ansell Ansell
Nitrile
Powdered (P)/ non-powdered (NP)
TT1Clear
P NP P
Synthetic elastomer
Biogel SkinsenseTM N
Regent1
NP
Swabsa
Johnson & Johnson Medical
TopperTM 12
–
a
1
Touch N Tuff1 Touch N Tuff1
P NP P NP
Each package contained two 5 by 5 cm sterile swabs. The swabs were impregnated with pentane during the experiments.
presented the least background noise and had the best efficiency in the collection of gasoline. Rolph [6] conducted the same type of study on five supports: nitrile, vinyl and cotton gloves, as well as cotton balls and cotton gloves under nitrile gloves. These supports were examined in terms of background interference and gasoline collection efficiency. Her research showed that the nitrile gloves were the most efficient in retaining fresh gasoline. The vinyl gloves produced good results; however they had high amounts of background interference. The other types of supports were shown to be ineffective in the collection and detection of gasoline on hands. On the basis of these two researches, a study was undertaken in order to analyze a much larger sample of collection supports using more sensitive analytical techniques. This is carried out in order to determine which support would best suit the set goals. The present study had two objectives. The first was to determine which procedure was the most effective in collecting and detecting the gasoline present on a person’s hands. The second was to elaborate a kit for sampling gasoline on arson suspects’ hands. 2. Materials and methods 2.1. Materials The three glove compositions most widely available on the market were selected; latex, nitrile and polyvinyl gloves were chosen, both in the powdered and the non-powdered versions. Gloves made of another synthetic elastomer and cotton swabs were also tested, resulting in a total of 16 different supports. Table 1 gives an overview of the different supports analyzed. The ignitable liquid used throughout the study was unleaded, regular-grade gasoline purchased from a local gas station. The chemicals used throughout the study (i.e., carbon disulfide for the desorption of the strips, 2-hexanone as the internal standard (IS), pentane and dichloromethane) were obtained from Fluka. 2.2. Instrumentation All of the obtained samples were analyzed with an Agilent Technologies 6890N gas chromatograph, coupled with an Agilent Technologies 5975 inert mass spectrometer. The following parameters were selected: Column: HP-5MS,
30 m 0.25 mm i.d. with 0.25 mm film thickness; carrier gas: helium at 1 ml/ min constant flow; inlet temperature: 250 8C; volume injection: 1 ml with 1:25 split ratio; oven program: 50 8C isotherm for 3 min, 5 8C/min up to 250 8C and 250 8C isotherm for 20 min; mass spectrometer ionization source at 230 8C; mass quadrupole analyzer at 150 8C in scan mode (m/z 10–450) with a sampling rate of 1.7 scan s 1. The robustness and repeatability of this method was monitored by periodic injections of a standard mixture of Restek E1618 Test Mix diluted in CH2Cl2 with a concentration of 0.005% (v/v) for each compound. Injections were performed during the whole duration of the study: once before the beginning of the study and once a week throughout the study. The RSD values obtained, indicated in Table 2, assess the robustness and repeatability of the method. The gas chromatography–mass spectrometry (GC–MS) apparatus was piloted with the Agilent MSD Chemstation (version D.02.00.275). The chromatograms and the mass spectra were visualized with the same software. Solvent controls were run before each analysis with the same solvent used for the analysis (CS2 or CS2 with 0.5% (v/v) 2-hexanone (IS)) to ensure that the solvent, the injection syringe, the injector and the column were not contaminated.
3. Experiment 3.1. Gasoline identification criteria The identification of gasoline throughout the whole study was carried out in agreement with the criteria recommended by the American Society for Testing and Materials (ASTM) E 161806 [7]. This standard states that the 4-peak group of C3alkylbenzenes [1-ethyl-3-methylbenzene and 1-ethyl-4-methylbenzene, 1,3,5-trimethylbenzene, 1-ethyl-2-methylbenzene, 1,2,4-trimethylbenzene] must be present, because it is found in 90% evaporated gasoline. Lighter components, namely the group of C2-alkylbenzenes (ethylbenzene and xylenes), were added as requirements for identification since the gasoline used in the experiments was ‘‘fresh’’, thus practically unevaporated. Moreover, two C4-alkylbenzenes were also considered: 1,2,4,5tetramethylbenzene and 1,2,3,5-tetramethylbenzene. In order to note the presence of gasoline, it was necessary for all the gasoline components cited to be present in the extracted ion chromatograms (EIC). Table 3 shows the target components of gasoline considered during this study.
Table 2 Percent relative standard deviations (RSD%) of peak areas for compounds of the standard Restek E1618 Test Mix calculated for five injections performed through the whole duration of the study. Compound
Toluene
p-Xylene
1-Ethyl-2-methyl-benzene
1-Ethyl-3-methyl-benzene
1,2,4-Trimethyl-benzene
C10
C12
C14
C16
RSD% [n = 5]
5.72
3.30
2.91
3.00
3.33
2.64
4.29
4.81
5.39
I. Montani et al. / Forensic Science International 194 (2010) 115–124 Table 3 Target compounds of gasoline. C2-alkylbenzenes
Ethylbenzene m-, p-Xylenea o-Xylene
C3-alkylbenzenes
Propylbenzene 1-Ethyl-3-methylbenzene and 1-ethyl-4-methylbenzenea 1,3,5-Trimethylbenzene 1-Ethyl-2-methylbenzene 1,2,4-Trimethylbenzene 1,2,3-Trimethylbenzene
C4-alkylbenzenes a
1,2,4,5-Tetramethylbenzene 1,2,3,5-Tetramethylbenzene
Unresolved peaks.
3.2. Establishment of calibration curves for the analytical method A calibration of the GC–MS method was undertaken in order to control and assess the linearity of the response of the detector for the analysis of the target compounds of gasoline presented in Table 3. For that, several known gasoline concentrations, combined with a fixed volume of internal standard, were injected (three times each) and analyzed in the same conditions as those employed during the experiments. The concentrations were selected in order to cover the whole range of concentrations likely to intervene later on during the tests, as suggested by Miller and Miller [8]. The coefficients of correlation (R) of all of the target compounds were significant after the application of the T-test (95%), done both before and after the calibration of the mass spectrometer (tune). However, a small improvement concerning the coefficient of regression was observed during the second analysis. 3.3. Evaluation of the background of the collection supports This first part of the project, concerning the choice of the supports, consisted in studying the volatile compounds the different collection supports might release. Indeed, some of the sample matrices may produce interfering volatiles, which could hinder subsequent identification process of ignitable liquid traces [9]. For that matter, the vapors produced by the tested supports during the heating process were studied using the technique of passive adsorption. The background noise generated by each support as well as its risk of interference with the profile of ignitable liquids (mainly gasoline) was evaluated by considering total ions chromatograms (TIC) and extracted ion chromatograms (EIC) for aromatic hydrocarbons (ions 91, 105, 106, 119, 120 and 134), alkanes (ions 57, 71 and 85) and alkenes (ions 55 and 69). The collection supports to be tested (a pair of gloves or the swabs) was placed in a nylon-11 type bag (obtained from BVDA, NL). A 1 dm3 frame (in the shape of a truncated cone) made of copper wire was also added inside of each bag, in order to maintain a reproducible analysis volume. An activated charcoal strip, part of a DFLEX device (obtained from Albrayco Laboratories Inc., USA), was hung above the sample. The bag was sealed with a tight knot, then heated in an oven at 60 8C during 16 h, using the technique of passive headspace concentration [10–12]. Finally, the activated charcoal strip was desorbed with 800 ml of carbon disulfide (CS2) and the solution was analyzed by GC–MS. Three pairs of each of the 16 collection supports were tested following this procedure, resulting in a total of 48 analyses. Blanks of the nylon-11 bags were analyzed in between each sample to ensure that the ovens were not contaminated. Only the supports that gave the best results in terms of background noise, in other words, the ones with the least
117
interfering volatiles, were kept for the second part of the study, where their efficiency in terms of collection of gasoline could be evaluated. 3.4. Efficiency of gasoline collection In this stage, the efficiency of the gloves and the swabs as means to collect gasoline on hands was tested. The adopted procedure was devised as to avoid as much contamination as possible (use of sterilized tools, no contact between the tester and the subjects, etc.). The four supports that were selected after the evaluation of background volatiles were studied under two perspectives. The first angle was to test their reproducibility concerning the collection of gasoline, when tested on a same person. This made it possible to evaluate the variations due to the method, the conditioning of the sample and the analysis which followed, while minimizing the influence due to the subject’s skin. Each support was tested three times on a same subject, totaling up to 12 analyses. In the second stage, each support was tested four times, each time on a different person. This made it possible to evaluate the variation of the capacity of collection of each support. The variation is due to the different types of skin of the subjects, their level of perspiration and other uncontrollable variables. For both experiments, 50 ml of gasoline was deposited using a micro-syringe (PerkinElmer, 50) in the right palm of the subject who proceeded to briefly rub his hands together. This was not carried out in a fumehood in order to avoid an unrealistic accelerated vaporization of the gasoline compounds. The subjects had not been in contact with any ignitable liquids in the last 48 h. Indeed, Darrer et al. [5] showed that after 120 min, the 500 ml of gasoline deposited on a person’s hand could not be detected according to the ASTM standards. The subject put on the gloves to be tested (which were deposited beforehand on a clean surface) and wore them for 20 min in a temperate room, following the conditions recommended by Darrer et al. [5]. The gloves were then placed in a nylon11 bag containing the metal frame of 1 dm3. An activated charcoal strip was added and the bag was sealed with a tight knot. The bag was then heated in an oven at 60 8C during 16 h, using the technique of passive headspace concentration. Finally, the activated charcoal strip was desorbed with 800 ml of carbon disulfide (CS2) with 0.5% (v/v) of 2-hexanone as internal standard. The eluate was analyzed by GC–MS. For the sampling with the swabs, 3 ml of pentane were dispersed on each one of the two swabs, which was then immediately rubbed on the palm, the fingers, the back of the hand and finally between the fingers. This was done until the pentane had completely evaporated (which corresponds to approximately 30–60 s). The operation was repeated on the other hand with the second swab. The swabs were then conditioned and sampled in the same way as the gloves. Each collection support was tested four times, each time on a different volunteer, giving a total of 16 analyses. 4. Results 4.1. Evaluation of the background of the collection supports The three chromatograms obtained for each type of gloves or swabs were examined. The compounds of gasoline, as well as the principal compounds of the other hydrocarbon classes described above, were searched for in each total ions chromatogram and its extracted ion chromatogram. The chromatogram obtained after the analysis of the nylon-11 bag blank gave the following peaks, in
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118
order of elution: acetone, carbon disulfide (CS2), benzene (all due to the solvent), followed by methylisobutylcetone (MIK), toluene and the limonene (all due to the nylon-11 bags). Given the presence of toluene, due to an external and non-controllable factor (the nylon-11 bags), this compound was not considered as a target compound during the study. Clearly, to take it into account would distort the interpretation of the results. The study of chromatograms of the background noise generated by the 16 supports tested allowed the following observations to be formulated: for each type of glove, the three analyzed pairs present qualitatively similar results with some small variations concerning the intensity of the peaks. The latex gloves gave in general much better results than the other types of gloves, which often presented series of alkanes. These alkanes are problematic because they interfere with a general search of hydrocarbons, since they are components of flammable substances of the ‘‘Heavy’’ class (such as kerosene and diesel). A quick overview of the main components observed for each type of tested support is presented in Table 4: In light of these results, the following gloves were retained for the subsequent part of the study: both of the VWRTM International latex gloves, in the powdered and non-powdered version, as well as the Sempercare1 edition latex gloves (non-powdered). All of the vinyl and nitrile gloves, as well as the gloves made of synthetic elastomer, were eliminated because of their strong production of volatile compounds interfering with the detection of small amounts of gasoline or other hydrocarbon classes such as the heavy petroleum distillates (kerosene, diesel, etc.). The TopperTM 12 medical swabs were also retained given that no volatiles were detected. Figs. 1–3 present the background noise of the non-powdered and powdered VWRTM International latex gloves and Sempercare1
edition latex gloves (non-powdered). Fig. 4 presents the background noise of the TopperTM 12 medical swabs and Fig. 5 the strong volatile profile obtained with the Semperguard1 nitrile gloves (non-powdered). 4.2. Collection efficiency of the retained supports In the first stage, the reproducibility of the developed method was tested with a deposition of 50 ml of gasoline, always on the hands of the same person, three times per each collection mean. This allowed the intravariability generated by each type of support to be evaluated by reducing as much as possible the parameters that could have an influence on the collection efficiency of the gloves (type of skin, perspiration, etc.). The area of each compound of interest on the area of the internal standard was calculated, giving a ratio (normalization). The results obtained appear in Fig. 6 (mean values and standard deviation) and Table 5 (relative standard deviation). Except for the TopperTM 12 swabs that also collected very few volatiles, an acceptable variation was observed for all the tested supports, showing that the reproducibility of the method was satisfactory. Once the reproducibility of the method was established, the efficiency of collection of each type of support could be evaluated. For each collection support, four samples were obtained with four different subjects and an initial amount of 50 ml of gasoline. The ratio of the area of each compound of interest, normalized to the internal standard was calculated in the same manner as above. Thus, the intervariability of the effectiveness of collection was estimated. The averages of the ratios of areas obtained, as well as the standard deviation calculated for each support, are presented below in Fig. 7.
Table 4 Main volatile compounds detected in the different studied collection supports. Collection support tested (brand) Latex
Powdered (P)/nonpowdered (NP)
Main volatile compounds detected
VWRTM International
P
VWRTM International Sempercare1
NP P
Sempercare1 edition
NP
Aromatics components of the C2 and C3 groups, as well a-pinene were present in trace in the Extracted Ion Mode N-alkanes from C10 to C14 were also present in very small quantities Both gloves presented chromatograms similar to those of VWRTM International, but with the a-pinene peak of strong intensity The powdered version presented, in addition, a strong peak of an aromatic derivative between C10 and C11 Presence of several peaks of strong intensity in the C10 to C14 range The chromatograms obtained showed several alkane peaks of great intensity in the C10 to C13 range (in a Gaussian distribution) C2 and C3 aromatic groups and a-pinene were present The chromatograms obtained were similar to the VWRTM International, with, in addition, the presence of a-pinene and a aromatic derivate between C10 and C11
Qualimed
Nitrile
Polyvinyl
1
P
Ansell Medical Gammex1
P
Sempermed1 supreme
NP
Semperguard1
P
Semperguard1 Ansell Touch N Tuff1
NP P
Ansell Touch N Tuff1
NP
Semperguard
1
P
C11 to C16 in the distinctive Gaussian distribution Alkane interferences and olefinic hydrocarbons were present in a significant number The powdered version had a series of aromatics between C15 and C19 The chromatograms obtained were very similar to the one obtained with the non-powdered Semperguard1 gloves
Strong presence of the C10 to C18 n-alkanes in a distinctive Gaussian distribution, characteristic of heavy petroleum distillates (kerosene, diesel) C2, C3 and C4-alkylbenzenes groups were slightly present. The chromatograms obtained were similar to the Semperguard gloves, with, in addition, a large amount of aromatic compounds between C10 and C15
Semperguard1 Maxxim Medical Europe TT1Clear
NP P
Synthetic elastomer
Biogel1 SkinsenseTM N Regent1
NP
Very badly defined base line due to the presence of alkanes and olefinic hydrocarbons Various aromatic compounds were present, but in small quantities.
Swabs
Johnson & Johnson Medical TopperTM 12
–
No volatiles detected
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119
Fig. 1. Chromatogram of the background noise of the non-powdered VWRTM International latex gloves with abundance scaled at 2 104; the full-scale chromatogram is presented in inclusion. The peaks marked with the asterisk glyph arise from the sampling bag and from the elution solvent.
Fig. 2. Chromatogram of the background noise of the powdered VWRTM International latex gloves with abundance scaled at 2 104; the full-scale chromatogram is presented in inclusion. The peaks marked with the asterisk glyph arise from the sampling bag and from the elution solvent.
On average, the non-powdered VWRTM International latex gloves gave the best results (Fig. 8), followed by the powdered VWRTM International gloves (Fig. 9), the non-powdered Sempercare1 gloves, then finally the TopperTM 12 swabs.
In order to evaluate the variations observed in the results, a statistical comparison was carried out with the software SPSS1 12.0. Multivariate analyses of the variance (Manova) were carried out on the ratios of the areas of all the gasoline compounds of each
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I. Montani et al. / Forensic Science International 194 (2010) 115–124
Fig. 3. Chromatogram of the background noise of the non-powdered Sempercare1 edition latex gloves with abundance scaled at 2 104; the full-scale chromatogram is presented in inclusion. The peaks marked with the asterisk glyph arise from the sampling bag and from the elution solvent.
support, to determine if a significant difference could be assessed between the different supports tested [13]. Although the nonpowdered VWRTM International gloves are on average almost twice more effective than the other supports tested, they
presented, with a confidence interval of 95%, no statistical difference with the other types of gloves. In fact, only the swabs were significantly less effective in the collection of the gasoline, compared to the powdered and the non-powdered VWRTM
Fig. 4. Chromatogram of the background noise of the TopperTM 12 medical swabs with abundance scaled at 2 104; the full-scale chromatogram is presented in inclusion. The peaks marked with the asterisk glyph arise from the sampling bag and from the elution solvent.
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Fig. 5. Chromatogram of the background noise of the Semperguard1 nitrile gloves (non-powdered) with abundance scaled at 1 106; the full-scale chromatogram is presented in inclusion. The peaks marked with the asterisk glyph arise from the sampling bag and from the elution solvent.
Fig. 6. Reproducibility of the method: for each collection support, three samples were collected from the same person. The figure depicts the mean values and standard deviations of the ratio of the target peak area to the internal standard area for each of the target gasoline compounds.
International latex gloves. No other statistically significant difference was observed. The small differences observed between the tested gloves could be due to differences they present in hydrocarbon permeability or in their capacity to make the skin perspire. The presence of talcum powder in some of the gloves could create a concurrent site for vapor adsorption and thus influence the amount of volatiles extracted by the passive headspace method. The important difference observed between the gloves and the swabs could be due to differences between the two collection processes such as the application time. Indeed, the gloves remained on the individual’s hands for 20 min,
whereas the swabs were applied less than 1 min on each hand, until the pentane had completely evaporated. In light of the results obtained on the interferences of the volatile products generated by the collection support, as well as the evaluation of their capacity and efficiency to collect gasoline, the non-powdered VWRTM International latex gloves were selected. In the optic of a swabbing kit, these gloves are recommended so far for collecting ignitable liquids on a person’s hands. As for the swabs, even though they generated no interferences, they were not retained on the basis of their low collection efficiency of gasoline during the tests.
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Table 5 Percent relative standard deviations (RSD%) of the normalized peaks of the target gasoline compounds for each collection mean. RSD% [n = 3]
Ethylbenzene p-, m-Xylene o-Xylene Propylbenzene 1-Ethyl-3(4)methylbenzene 1,3,5-Trimethylbenzene 1-Ethyl-2-methylbenzene 1,2,4-Trimethylbenzene 1,2,3-Trimethylbenzene 1,2,4,5-Tetramethylbenzene 1,2,3,5-Tetramethylbenzene
Non-powdered VWR International latex gloves
Powdered VWR International latex gloves
Non-powdered Sempercare latex gloves
Topper 12 Medical swabs
17.66 22.12 22.52 33.44 34.55 34.39 33.69 33.68 29.54 27.37 23.40
10.64 10.18 10.02 7.57 7.27 8.81 9.31 7.70 9.92 7.66 7.44
25.03 24.07 28.63 26.22 27.77 28.38 29.46 27.83 28.23 27.85 27.44
44.04 43.34 55.35 42.36 56.02 56.88 62.36 64.83 69.90 68.68 76.44
4.3. Development of a sampling kit Once the optimal support was chosen, a sampling kit for use on people suspected of illegal involvement with ignitable liquids was developed. The authors were inspired by the study conducted by Wallace and McKeown, who developed sampling procedures for firearms and explosives residues [14]. The kit had several objectives: it had to be compact and practical, present an ease of use and preparation, and, most importantly, it had to be the least susceptible to any exterior contamination. The collection supports had to have the best collection efficiency and the least background noise possible. With these elements in mind, a prototype suspect sampling kit was designed and tested successfully. The kit is contained in a multilayer DUO-GASBAGS bag (obtained from KTM-Krim Teknisk Materiel AB, Sweden) that is divided into three parts with the help of a thermal sealer. The separation into three compartments minimizes the risk of cross-contaminations between each section. The first section of the kit contains a first pair of VWRTM International non-powdered gloves to be worn by the sampler, along with comprehensive instructions. The second part contains a pair of VWRTM International non-powdered gloves that consists of the blank sample, a nylon-11 bag, a technical form to be filled out by the sampler and a paperclip. These gloves are to be placed in the sampling area, while the sampling of the suspect is carried out, and thus provide a control sample of both the sampling environment as well as of the conditioning and storage of the kit. The third section of the kit contains the sampling material, i.e.
a second pair of VWRTM International non-powdered gloves, a nylon-11 bag, a technical form and a paperclip. This pair of gloves is the closest possible to the blank gloves in terms of origin (they are taken from the same lot) and storage conditions, to ensure optimal control conditions. The kit can finally be integrated in a metal paint can, closed hermetically and sealed with an instructive label. The use of a metal can makes it possible to overcome a great disadvantage associated with the use of a multilayered bag only: the storage of the kits in places that can present contaminations, such as, for example, in cars. Indeed, the metal boxes present an additional impermeability to those of the bags alone, as well as a mechanical barrier to perforations that bags can be subject to. 4.4. Using the kit Before opening the kit, several precautions should be observed by the sampler: they can be stated on the outer label. Their purpose is to minimize any contamination that could occur during the sampling and conditioning phase, such as sampling in an environment contaminated with a ignitable liquid. The sampler proceeds by opening the metal can, and taking out the multilayer bag. He/she opens it on the designated side, puts on his/her pair of gloves, then takes out the control sample gloves and puts them in the nylon-11 bag. This bag is left open during the whole swabbing process and is latterly sealed. The sampler then gives the sampling gloves to the suspect, who proceeds to put them on himself/herself and wears them for
Fig. 7. Efficiency of collection: a group of four persons was considered. For each collection support, one sample was collected on each member of the group, giving a total of four samples per support. The figure depicts the mean values and standard deviations of the ratio of the target peak area to the internal standard area for each of the target gasoline compounds.
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Fig. 8. Chromatogram of one collection test undertaken with the non-powdered VWRTM International latex gloves with abundance scaled at 7 104. The peaks marked with the asterisk glyph arise from the sampling bag and from the elution solvent; two other peaks (IS) arise from the internal standard added to the elution solvent.
Fig. 9. Chromatogram of one collection test undertaken with the powdered VWRTM International latex gloves with abundance scaled at 7 104. The peaks marked with the asterisk glyph arise from the sampling bag and from the elution solvent; two other peaks (IS) arise from the internal standard added to the elution solvent.
20 min. The suspect then takes off his gloves himself by unrolling them and places them in the nylon-11 bag. The sampler then seals the bag by making a double knot and annexes
the form to the bag. Both samples (the control and the suspect sample) are to be transmitted to a laboratory as quickly as possible for analysis or to be stored in a refrigerator, avoiding
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contact between both samples. It is also suggested to remove the suspect’s clothes and shoes for a complementary ignitable liquid analysis, as recommended by Coulson and Morgan-Smith [4]. 5. Discussion During the study of the intravariability of the gasoline collection from the tested supports, small differences were recorded. They could be due to several factors, such as the conditions under which the swabbing took place (primarily the temperature), losses that occurred during the adsorption and desorption of the compounds on the activated charcoal strip. The study of the efficiency of collection made it possible to note that, except for the Sempercare1 edition gloves, the gasoline collection efficiency of the supports on different people (intervariability) presented a greater variation than the results obtained for the collection on a same person (intravariability). These differences are primarily due to the factors referred to above, as well as other external factors, such as differences in the types of skin and perspiration of the subjects. The non-powdered VWRTM International latex gloves had the best results in terms of gasoline collection at the time t = 0. The possibility that another type of support would be more effective than the latex gloves after a certain amount of time cannot be ruled out. Indeed, the pentane-soaked swabs could be more suited to the collection of the gasoline after a certain amount of time has passed, pentane presenting a better affinity with the heavier compounds. Moreover, the compress could be employed in sequence after the gloves are worn. This method is all the more interesting since suspected arsonists are seldom stopped immediately after having committed the crime. A certain amount of time has already elapsed. On the other hand, it could be more convincing, from an interpretative point of view, to find light compounds, since their persistence is less than that of heavier compounds. The developed sampling kit also has the advantage of providing the sampler with a blank swab. This blank originates from the same pack as the gloves used for swabbing the suspect and is handled and stored under the same conditions as the latter. The blank also allows the swabber to obtain a blank of the environment in which the swabbing takes place. 6. Conclusion This research was directed toward the study of collection of ignitable liquids on arson suspects’ hands, implying the use of accelerants. The purpose of this work was to determine the best method for collecting and detecting gasoline on a suspect’s hands and to advise the development of a simple and effective sampling kit. Sixteen swab collection supports were evaluated, on the criteria of their background noise and their effectiveness in the collection of gasoline. The volatiles that emanated from the collection supports were analyzed by GC–MS after a passive headspace extraction procedure. Only four collection supports offered acceptable levels of background contamination: three types of
latex gloves and sterile medical swabs. These four collection supports were then tested to see which was the most effective in the collection of gasoline on hands. Although the non-powdered VWRTM International latex gloves were not statistically better than the other types of supports tested, they showed the best average during the tests and were therefore selected for the sampling of ignitable liquids on hands. This information allowed the authors to develop a prototype of a simple and effective kit for the sampling of ignitable liquids on arson suspects’ hands. The main goals set before the establishment of the kit were respected. The developed kit is easy to use, practical, compact and in terms of storage and all precautions were taken in order to minimize external contaminations due to storage, transport and manipulation. Acknowledgement We acknowledge Mr Eric Stauffer whose comments greatly improved this manuscript. References [1] W. Bertsch, G. Holzer, C. Sellers, Chemical Analysis for the Arson Investigator and Attorney, Huethig Buch Verlag, 1993. [2] E. Stauffer, J.A. Dolan, R. Newman, Fire Debris Analysis, Academic Press, 2007. [3] J.D. DeHaan, Kirk’s Fire Investigation, 5th ed., Prentice Hall, Brady, 2002. [4] S.A. Coulson, R.K. Morgan-Smith, The transfer of petrol on to clothing and shoes while pouring petrol around a room, Forensic Science International 112 (2–3) (2000) 135–141. [5] M. Darrer, J. Jacquemet-Papilloud, O. Dele´mont, Gasoline on hands: preliminary study on collection and persistence, Forensic Science International 175 (2–3) (2008) 171–178. [6] E. Rolph, Petrol on Hands: Handling Method and Validity of Results, Department of Chemistry, University of Technology, Sydney, 2000. [7] ASTM, E1618-06: Standard test method for ignitable liquid residues in extracts from fire debris samples by gas chromatography-mass spectrometry 1, Annual ASTM Standards on Disc, vol. 14.02, 2007, American Society for Testing and Materials. [8] J.N. Miller, J.C. Miller, Statistics and Chemometrics for Analytical Chemistry, 5th ed., Pearson Education Limited, Harlow, England, 2005. [9] A.D. Pert, M.G. Baron, J.W. Birkett, Review of analytical techniques for arson residues, Journal of Forensic Sciences 51 (5) (2006) 1033–1049. [10] J.F. Demers-Kohls, S.L. Ouderkirk, J.L. Buckle, W.E. Norman, N.S. Cartright, C. Dagenais, Evaluation of the DFLEX device for fire debris analysis, Journal of the Canadian Society of Forensic Science (1994) 99–123. [11] R.T. Newman, W.R. Dietz, K. Lothridge, The use of activated charcoal strips for fire debris extractions by passive diffusion. Part 1: The effects of time, temperature, strip size, and sample concentration, Journal of Forensic Sciences 41 (3) (1996) 361–370. [12] ASTM, E1412-00: Standard practice for separation of ignitable liquid residues from fire debris samples by passive headspace concentration with activated charcoal, Annual ASTM Standards on Disc, vol. 14.02, 2007, American Society for Testing and Materials. [13] J. Bray, S. Maxwell, Multivariate Analysis of Variance, Sage University Paper Series on Quantitative Research Methods, 1985, p. 54. [14] J. Wallace, W. McKeown, Sampling procedures for firearms and/or explosives residues, Journal of Forensic Science Society 33 (1993) 107–116. [15] F. Terrapon, J. Papilloud, E. Du Pasquier, J. Martin, Persistence of gasoline on jeans, in: First European Meeting of Forensic Science, Lausanne, September 17–19, 1997. [16] T. Folkman, A. Kuehl, R. Groves, A. Beveridge, Evaporation rate of gasoline from shoes, clothing, wood and carpet materials and kerosene from shoes and clothing, Canadian Society Forensic Science Journal 23 (2 & 3) (1990) 49–59.