Forensic Identification of Gasoline Samples D.A. Birkholz 1, Michael Langdeau 1, Preston Kulmatycki, 1 and Tammy Henderson 1. Enviro-Test Laboratories, Edmonton, AB. Abstract Gasoline samples (premium and regular grade) from the five major Western Canadian refineries were obtained and analyzed using high resolution gas chromatography/mass spectrometry (HRGC/MS). Reference compounds containing n-paraffins, isoparaffins, naphthenes, olefins, and aromatics were obtained from Supelco (P-I-A-N-O ) and analyzed using HRGC/MS to facilitate identification of compounds. In order to mimick the effects of weathering, an aliquot of the reference fuel was extracted with water and the water phase further extracted with pentane. The weathered gasolines samples were also subjected to HRGC/MS analysis. Data obtained from both weathered and unweathered gasoline samples was reviewed and pairs of compounds chosen based on 1) similar boiling point, 2) complete chromatographic resolution from interfereing compounds and 3) presence in all grades of gasoline whether weathered or unweathered. Chromatographic peaks representative of the chosen compounds were integrated and a ratio obtained. The resulting ratios were plotted using an Excel radar plot to generate distinctive shapes. These shapes were adjusted by the application of appropriate multiplication factors to spread out the data. The shapes were compared to one another to determine whether sources of gasoline (both weathered and unweathered) could be distinguished from the shape obtained using the Excel radar plot. This type of approach was applied successfully several years ago to avaiation fuel as part of an investigation involving litigation and was presented at the ETL Seminars in 2001. Our purpose of this research was to determine whether such an approach could be applied to weathered gasoline and whether such an approach might be useful in reclamation to determine the sources of fuels. Introduction Remediation of hydrocarbon contaminated sites continues to present challenges to many engineering consulting firms. Often times the source of such contamination may be several differing suppliers of fuel. Although Phase I audits are usually successful in depicting the history of a contaminated site, such audits cannot determine if one or more parties are responsible for the observed contamination.
Determining the refining source of weathered gasoline can be very difficult. Table 1 summarizes various methods which have been suggested Table 1 Summary of Procedures Used to Fingerprint Fuel Method Description Advantage / Disadvantage Gas TPH, method 8015, 8270 total Good for source matching; weathered fuels problematic chromatography/fid/pid/ms extractables Gas chromatography / BTEX, total purgeables, method Good for source matching; weathered fuels problematic headspace/purge and trap/fid/pid/ms 8240, 8260 Metals lead, vanadium, nickle Based on leaded gas and on crude Lead phased out, crude stocks for refineries change stock Oxygenated blending agents Analysis for alcohols and ethers Effect of weathering unknown, blending agents may change Ethylene dichloride and Lead scavengers used in leaded gas Leaded gas phased out; useful in historical remediations ethylene dibromide Methyl-t-butyl ether Improve octane rating and improve Amount relative to source and effect of weathering unknown emissions Dye additives, diphenyl Analysis for specific dyes and sulfur Effect of weathereing unknown. Consistency unknown disulphides Analysis for alkylated aromatics High resolution gas chromatographic analysis/fid/ms compounds GC/MS analysis for select compounds followed by principle component analysis of the data CAN/CGSB 3.0 No. 14.3 analysis on 100 m PONA column May have promise used in arson cases Good for source matching; weathered fuels problematic Octane index Iso + T/nC 7 + nc 8 Effect of weathering unknown Two dimension GC High resolution analysis Effect of weathering unknown Isotopic ratios 13 C/ 12 C, D/H, 34 S/ 32 S May have promise
The application of gas chromatography/mass spectrometry analysis followed by quantification of select alkylated aromatic compounds (alkylated naphthalenes) was found to be very useful in arson investigations, especially if the data was analyzed using principle component analyses (Sandercock and Du Pasquier, 2003). The premise of this method is that specific ratios of select hydrocarbons in a fuel source are unique and transgress weathering. The unique ratios are a function of refinery processes and as such may be useful in identifying sources of gasoline. We had used a similar approach in a remediation investigation involving jet fuels and diesel fuel and found this procedure to be very useful in depicting sources of contamination (Birkholz, 2001). The purpose of this investigation was to obtain gasoline samples (premium and regular grade) from five refineries from Western Canada and to determine 1) whether the sources of gasoline be uniquely identified using forensic methods, and 2) wether weathered samples from these same refineries be correlated with the appropriate source. Methods Gasoline samples (premium and regular) were obtained from the following refineries: Chevron, Vancouver; Husky, Prince George; Petro Canada, Edmonton; ESSO, Edmonton and Shell, Edmonton. A weathered sample was prepared by adding 2 ml of gasoline to 10 ml of tapwater. The mixture was subjected to vortex/sonication and an aliquot (5 ml) of the water phase was carefully removed. Two ml of pentane was added to the water phase (5 ml) and subjected to vortex/sonication. The resulting pentane was removed and subjected to chemical analysis. Chemical analyses of gasoline samples along with weathered samples was performed using gas chromatography/mass spectrometry. Separation was performed using a 100 m x 0.25 mm Petrocol DH column and compound identification was facilitated by the analysis of a PIANO mixture of compounds obtained from Supelco, Inc. Mass spectra of the individual compounds were retrieved and compared with the retention times of the PIANO mixture to confirm compound identification. Table 2 summarizes the compounds selected for analysis along with the ions monitored to obtain extracted ion-current profiles. The areas associated with the ion-current profiles were used to obtain ratios. Each ratio was multiplied or divided by a specific factor to facilitate plotting the data using Excel radar. The multipliers were used to spread the shapes of the plots.
Table 2 Summary of compounds used, factors applied and ions monitored. Compound Ratio Ions Monitored, m/z Decane/Indane * 2 57/117 1-methyl-4-ispropylbenzene/Indane * 10 119/117 1-methyl-2-ispropylbenzene/Indane * 40 119/117 1-methyl-3-n-propylbenzene/Indane * 2 105/117 1-methyl-4-n-propylbenzene / 2 105/117 Naphthalene/1,2,4,5-Tetramethylbenzene / 2 128/119 methylnaphthalene/1,2,4,5-tetramethylbenzene / 2 142/119 Dodecane/naphthalene * 10 57/128 Results Figure 1 shows radar Excel plots for premium gasoline compared to weathered premium gasoline. From this figure it is apparent that 1) profiles for premium gasoline obtained from the five Western refineries are distinctly different and therefore can be differentiated from one another; 2) profiles for weathered premium gasoline samples, although not exact, are similar to unweathered fuel and hence allow for identification of fuel source. Figure 2 shows radar Excel plots for regular gasoline compared to weathered regular gasoline. From this figure it is apparent that 1) profiles for regular gasoline obtained from the five Western refineries are distinctly different and therefore can be differentiated from one another; and 2) profiles for weathered regular gasoline samples, although not exact, are similar to weathered fuel and hence allow for identification of fuel source. Radar plots obtained for each refinery, comparing weathered premium and regular gasoline to pure product showed similar profiles, however plots were not exactly superimposable.
Conclusion High resolution GC/MS analysis followed by the selection of select hydrocarbons (saturates, alkylated benzenes, and naphthalenes), followed by specific ratio plots using Excel radar, resulted in unique plots for gasoline obtained from the five Western refineries. Using this technique, free product could be referenced to a refinery source because each refinery displayed a unique and distinctive radar plot. Weathered gasoline, i.e. water soluble fraction as might be found in a reclamation pieziometer, gave rise to distinctive radar plots revealing that environmental samples could be delineated as similar or different. Although some differences in radar plots were observed relative to fresh gasoline, profiles were generally similar allowing for product source identification. Although the experiments conducted here were considered a success there is concern that refining processes change with time resulting in differing radar plots. Furthermore, the influence of soil in the partitioning of hydrocarbons raises concerns as to the validity of this method for the forensic identification of contaminated soils. At present we have collected more gasoline samples from the same refineries and have initiated soil weathering studies. Analysis of the data will provide further insight of the utility of this method to general reclamation intiatives. References: 1. Sandercock, P.M.L., and E. Du Pasquier (2003). Chemical fingerprinting of unevaporated automotive gasoline samples. Forensic Science International, 134: 1-10 2. Birkholz, D.A. (2001). Forensic chemical analysis of petroleum products: its not just lead anymore. ETL seminar, February 27, 2001, Sheraton Cavalier, Calgary, Alberta.
Acknowledgements The authors wish to thank Enviro-Test Laboratories for funding this research initiative.
Figure 1 Radar Plot of Premium and Weathered Premium Gasoline Premium Gasoline 0.4 0.2 0 Chevron Vancouver Premium Husky Prince George Premium Petrocanada Edmonton Premium ESSO Edmonton Premium 2 Shell Edmonton Premium 1.8 1.6 Weathered Premium 1.4 1.2 1 0.8 0.6 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 Figure 1 Radar Plots for Premium and Weathered Premium gasoline
Regular Gasoline 1.6 1.4 1.2 1 0.8 Chevron Vancouver Regular Husky Prince George Regular Petrocanada Edmonton Regular ESSO Edmonton Regular Shell Edmonton Regular Weathered Regular 0.6 0.4 0.2 0 2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 Figure 2 Radar Plots for regular and weathered regular