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Fast Analysis of Fire Debris Using an Agilent 5975T LTM GC/MSD with Capillary Trap Sampling (CTS)


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Fast Analysis of Fire Debris Using an Agilent 5975T LTM GC/MSD with Capillary Trap Sampling (CTS) Application Note Author Suli Zhao Agilent Technologies (Shanghai) Co., Ltd Abstract This application note
Fast Analysis of Fire Debris Using an Agilent 5975T LTM GC/MSD with Capillary Trap Sampling (CTS) Application Note Author Suli Zhao Agilent Technologies (Shanghai) Co., Ltd Abstract This application note describes the development of an innovative method for the confirmation of fire accelerants using the Agilent Capillary Trap Sampler (CTS), which is based on capillary column absorbing principles. CTS has the advantage of rapid sampling of airborne debris and toxic compounds within 1 minute. The study used 97 RON (Research Octane Number) octane gasoline as a standard, and compared the aromatic compounds (m/z = 91) in the sample to those in the standard in order to qualify the accelerant type. Results confirmed that this is an effective method for confirming accelerant types. Trap head Trap columns Introduction Arson is a crime that can cause serious property damage, injury, and sometimes death. Fires of suspicious origins are investigated to determine whether or not the cause was intentional. Laboratory analysis of fire debris can be used to search for traces of accelerants that could have been used to start a fire. These include: gasoline, kerosene, diesel, heating oils, alcohols, and mineral and white spirits. Samples of debris from fires are routinely analyzed for traces of hydrocarbon accelerants. Mass spectrometery is used to identify and eliminate the interference of pyrolysis products in the resulting chromatograms. The hydrocarbon type is determined by comparing the sample chromatogram to standards. Individual mass chromatograms of key ions are typically reviewed to make this comparison. However, a good comparison is not always possible because the sample is severely fire damaged making it difficult to get a sample. Therefore, sample collection is a critical step preceding analysis. The samples must be collected from the fire origination point because this is the only place where traces of accelerant, if used, would be found. Before the development of CTS, Solid Phase Microextraction (SPME), has been the scientific choice for sample collection. One advantage of SPME is that it has good concentrating ability [1]. However, it also has the disadvantage of requiring more than 30 minutes to aquire a trace content sample. This study details the development of an airborne sampling technique using CTS based on the same principles as SnifProbe [2]. CTS can process a sample within a few seconds to several minutes and it can easily be used on-site. One sample can be analyzed within minutes using an Agilent 5975T LTM GC/MS System. Since gasoline is a common fire accelerant, this study attempted to identify gasoline in fire debris samples. CTS is a 6-port trap column airborne sampler. It can accommodate six trap columns simultaneously with different polarities. Customized column selection provides more flexibility in application. This application note explores using a Pora PLOT Q column as the trap column. The performance evaluation is compared to the Shanghai Key Laboratory of Crime Scene Evidence, Institute of Forensic Science s conventional SPME method. The verification tests were done by six Shanghai fire stations. Experimental Reagents and chemicals All the chemicals used in this study are from Shanghai Key Laboratory of Crime Scene Evidence, Institute of Forensic Science. Commonly used fire accelerants: 97 RON gasoline, kerosene, and small organic solvents. Equipment and materials The analysis was performed on an Agilent 5975T LTM GC-MS equipped with TSP (G4381A). The sample was prepared using a CTS system, and the compounds were separated on an Agilent HP-5 ms LTM column, 10 m 0.18 mm, 0.18 µm). Instrument conditions Table 1. Instrumentation and Conditions of Analysis Instrumentation GC/MS system Agilent 5975T LTM GC/MS System Inlet Split/splitless, with TSP Column Agilent HP-5ms LTM 10 m 0.18 mm, 0.18 µm Guard column 1 m deactivated blank column connected to the injector. Experimental conditions Inlet temperature 220 C Injection mode Split, 20:1; manual Carrier gas Helium Constant flow 1.4 ml/min LTM oven temperature 40 C (0.8 minutes), 12 C/min, 50 C (0.4 minutes), 30 C/min, 100 C (0 minutes), 90 C/min, 180 C (0 minutes), 120 C/min, 220 C Transfer line temperature 230 C Ion source 230 C Quad. temperature 150 C Ionization mode EI Scan mode full scan, m/z u EMV mode Gain factor Gain factor 5.00 Resulting EM voltage 1,430 V Solvent delay 0.1 minutes 2 Sample preparation The sample was prepared using direct headspace gas sampling with CTS. A specific volume of liquid gasoline was injected into a 5-L glass bottle, then equilibrated for six hours to vaporize the gasoline components. Results and Discussion Trap column selection and CTS work conditions optimized This study required a short trap column with sufficient absorbing volume. Therefore, a Pora PLOT series column was selected. To match the Agilent standard ferrules, we used 0.32-mm and 0.53-mm columns as trap columns. Considering the micro vial height and ease of removal, 20-mm columns are suitable. Therefore, an Agilent Pora Plot Q column (20 32 mm, 20 µm) was chosen because it can absorb most components in gasoline. CTS pump test conditions were 60 ml/min for 1 minute because these settings produce good results for the samples tested. Identification of gasoline Gasoline is a mixture of hydrocarbons, although some may contain significant quantities of ethanol and some may contain small quantities of additives such as tertiarybutylmethyl ether as agents to increase the octane rating. The hydrocarbons consist of a mixture of n-paraffins, naphthenes, olefins, and aromatics. Naphthenes, olefins, and aromatics increase the octane rating of the gasoline whereas the n-paraffins have the opposite effect. The aromatics consist mostly of a mixture of benzene, toluene, and xylenes. The gasoline composition can vary significantly depending on the source of the crude oil, its processing method, and its intended use. Because aromatic compounds are a typical specification marker of gasoline, this study used aromatic compounds as the main specification for identification of gasoline. We compared the components of the samples to gasoline standards. Gasoline standard preparation A 1-µL amount of 97 RON octane gasoline was placed in a 5-L glass bottle to vaporize. After vaporization, 60 ml of headspace air were sampled. Figure 1 shows the total ion chromatogram (TIC) of the gasoline. As the figure illustrates, almost all visible peaks were aromatics. Table 1 lists the main trapping components of gasoline. Components were identified with the assistance of the AMDIS software in NIST EPA library. The AMDIS software allows some overlap peaks to be ignored, and the rapid 5975T method to be used Figure Time TIC of 97# gasoline with six columns Table 1. Main Trapping Components of 97# Gas Oil (Identified by AMDIS-NIST EPA Library) RT (min) Chemical name CAS no Cyclohexane Benzene Hexanol, 2-ethyl Penten-2-one, 4-methyl Toluene Methanethiol Ethylbenzene Benzene, 1,3-dimethyl p-xylene Benzaldehyde o-xylene Hexanol, 2-ethyl Benzene, propyl Benzene, 1,2,4-trimethyl Propane, 2-methoxy-2-methyl Benzene, (1-methylethyl) Benzene, 1,3,5-trimethyl Decane Indane Indene Benzene, 1-methyl-4-(1-methylethyl) Benzene, 1-methyl-2-propyl Benzene, 1-methyl-3-propyl Decane, 4-methyl Benzene, 1-methyl-2-(1-methylethyl) Benzene, butyl Benzene, 1,2-diethyl Benzene, 1,2,3,4-tetramethyl RT (min) Chemical name CAS no Decane, 2-methyl Benzene, 1,3-diethyl Benzene, 1-ethyl-2,4-dimethyl Benzene, 1-methyl-3-(1-methylethyl) Undecane (ID#: ) Benzene, 1-ethyl-2,3-dimethyl- (ID#: ) Benzene, 1-ethyl-3,5-dimethyl- (ID#: ) Benzene, 1,2,4,5-tetramethyl H-Indene, 2,3-dihydro-5-methyl H-Indene, 1-methyl Benzene, 1,2,3,5-tetramethyl Naphthalene Benzene, pentamethyl Dodecane Benzene, 1,3-dimethyl-5-(1-methylethyl) H-Indene, 2,3-dihydro-4,7-dimethyl Naphthalene, 2-methyl Tridecane Biphenyl Tetradecane Naphthalene, 1-ethyl Naphthalene, 1,5-dimethyl Naphthalene, 1,8-dimethyl Naphthalene, 1,4-dimethyl Naphthalene, 1,3-dimethyl Butylated Hydroxytoluene Naphthalene, 1,6,7-trimethyl Compare CTS method with their conventional lab method In China, a SPME method with GC/MS is the forensic standard. The sample preparation time is 40 minutes and the GC/MS running time is 40 minutes with a VF-5ms (30 m 0.25 mm, 0.25 µm). Using an Agilent 5975T GC/MS with an HP-5ms column (10 m 0.18 mm, 0.18 µm), we were able to reduce the running time approximately 5 fold. The CTS method requires only 1 minute, which is an improvement in sample preparation. Figure 2 is a TIC and EIC chromatogram of a SPME method for gas oil. All of the main components can be aligned using either method. Therefore, a CTS sampling technique can replace SPME in practical applications. Real case study Several real samples from the field provided by the Shanghai forensic institute were tested in this study. User reports were provided by several fire stations. In these reports, CTS was successfully used for gasoline, banana oil samples, and so forth. It was determined that all of the main components from fire debris caused by gasoline could be matched with the gasoline standard. Gasoline identification in fire debris A special group in gasoline is aromatic compounds, such as toluene and xylenes with short arms to long arms. They all have the characteristic ion m/z 91. These masses are the molecular weights of the most abundant aromatic compounds found in the gasoline. The aromatic compounds were compared as they are the most characteristic compounds in gasoline. There is no extra solvent wash step and only airborne samples were used in the CTS sampling technique, so there was minimal interference in the GC/MS chromatogram with a low matrix effect. This advantage provides a good basis for gasoline identification. Figure 3 is an overlap EIC of gasoline standard and gasoline residue from fire debris. The black chromatogram (big) is a typical gasoline chromatogram and blue (small) is sample. Burned denim was the fire sample used for analysis. Figure 3 shows good correlation of the two chromatograms. Comparing the components relative contents and types shows that the fire was caused by gasoline. GCounts GCounts A B Figure 2. SPME results for 97# gasoline. A) TIC and B) EIC of m/z Figure 3. Mass chromatograms of fingerprints of gasoline (m/z 91). Gasoline standards (black) and fire debris caused by gasoline (blue) Banana oil identification Banana oil, also called thinner, is often used as a paint dilution. Since it is readily available, it is often used as a fire accelerant. Its main components are xylenes and some butyl acetates. The primary distinction between gasoline and banana oil is the content of xylenes. Banana oils typically have a high content of xylenes, as well as butyl acetates. The CTS technique allowed direct sampling for one minute. Two trap columns were injected into the GC/MS. Figure 4 shows an overlap EIC of the gasoline standard and banana oil. CTS helped provide a good backup for crime evidence. Extended applications of CTS CTS can also be applied to the detection of aviation kerosene and diesel. Figure 5 presents a TIC of diesel and Figure 6 gives a TIC of aviation kerosene. Table 2 shows the light components of diesel, and Table 3 lists the light components of aviation kerosene Figure Mass chromatogram of banana oil and gasoline (m/z 91), banana oil (blue), gasoline (black). Both are samples from the field. Abundance Figure 5. TIC of diesel by CTS sampling. Abundance Figure 6. TIC of aviation by CTS sampling. 6 Table 2. Light Components of Diesel Table 3. Light Components of Aviation Kerosene R.T. (min) Chemicalname n-hexane ,2,4-Trimethylpentane Methylhexane Methylcyclohexane Toluene Methylheptane n-octane Octanol Ethylbenzene m-xylene Methyloctane o-xylene n-nonane n-propylbenzene m-ethyltoluene Methylnonane o-ethyltoluene ,3,5-Trimethylbenzene n-decane Isopropylbenzene sec-butylbenzene p-isopropyltoluene n-undecane tert-butylbenzene n-dodecane n-tridecane n-tetradecane n-pentadecane ,6-di-t-Butyl-4-methylphenol(BHT) R.T. (min) Chemical name Acetaldehyde n-hexane Methylpentane Methylcyclohexane Octene Methylhexane Methylheptane n-octane Ethylbenzene m-xylene Methyloctane n-nonane Isopropylbenzene Ethyl-1-hexanol n-propylbenzene m-ethyltoluene Methylnonane Decene ,3,5-Trimethylbenzene n-decane o-ethyltoluene o-methystyrene n-butylbenzene Toluene sec-butylbenzene p-isopropyltoluene n-undecane tert-butylbenzene Naphthalene n-dodecane n-tridecane n-tetradecane ,6-di-t-Butyl-4-methylphenol (BHT) 7 Conclusion Capillary Trap Sampling (CTS) allows a direct comparison of standard compounds to hydrocarbons and other organics vaporized from burned material samples, to determine the type of accelerant used in a fire. An excellent correlation can be obtained, since the matrix compounds of the sample can be eliminated by the selectivity of CTS sampling with the transportable Agilent 5975T LTM GC/MSD. The CTS airborne sampling technique and 5975T GC/MSD technology provides a fast and reliable method for fire accelerant identification. Reference 1. J.A. Lloyd and P.L. Edmiston Preferential Extraction of Hydrocarbons from Fire Debris Samples by Solid Phase Microextraction J. Forensic Sci. Jan. 2003, Vol. 48, No. 1. For More Information These data represent typical results. For more information on our products and services, visit our Web site at Agilent shall not be liable for errors contained herein or for incidental or consequential damages in connection with the furnishing, performance, or use of this material. Information, descriptions, and specifications in this publication are subject to change without notice. Agilent Technologies, Inc., 2013 Printed in the USA December 12, EN
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