Forensic Fingerprinting of Diamondoids for Correlation and Differentiation of Spilled Oil and Petroleum Products

Abstract

Diamondoids (adamantanes and diamantanes) are rigid, three-dimensionallyfused cyclohexyl-ring alkane compounds that can be found in almost all crude oils and in most petroleum products. Forforensic environmental investigations, the most commonly used biomarkers are high molecular weight (MW) tri- to pentacyclic terpanes and steranes. Most of these high MW biomarkers, however, are removed from the original crude oil feedstocks during the refining processes, while smaller biomarkers including diamondoids are concentrated in petroleum products. Fingerprinting diamondoids could thus provide another diagnostic means for correlation and differentiation of spilled oils and be particularly valuable for light to midrange distillates, such as jet and diesel fuels, the source of which may be difficult to identify using routine biomarker techniques. In this work, a reliable GC-MS analytical method has been developed for characterization and quantitation of diamondoids. The method detection limits for five target diamondoids were determined to be in the range of 0.06-0.14 microg/g oil. Distributions of diamondoids in over 100 different oils and refined products were quantitatively compared. The concentrations of four groups of target biomarkers were found, in general, to decrease in the order of sesquiterpanes > terpanes and steranes > adamantanes > diamantanes in both crude oils and refined products. A number of indices of admantanes and diamantanes have been developed and assessed as source indicators using their diagnostic powers (DP). The effects of evaporative weathering and biodegradation on alteration of diamondoid distributions have been quantitatively investigated. Finally, a spill case study by statistical evaluation of diagnostic ratios using the "two-tailed" Student's tapproach is presented to illustrate the unique utility of diamondoids for correlation and differentiation of unknown spilled diesels.

Quantitative analysis of diamondoids in crude oils using gas chromatography–triple quadrupole mass spectrometry

“…2, where it can be seen that the individual peaks of diamondoid hydrocarbons are well separated without significant interference from the background, except for a few diamantane compounds (i.e., diamantane, 1-methyldiamantane) of the well TD2 oil. Similar to the method of Wang et al (2006), the RRFs obtained from adamantane (A), 1-MA, 2-MA, 1-EA, 2-EA, diamantane (D) are used for quantitation of adamantane (A), 1-MA, 2-MA, 1-EA, 2-EA, diamantane (D) in crude oils; the RRFs from 1,3-DMA, 1,3,5-TMA and 1-E-3-MA for quantitation of di-, tri-, and tetra-methyladamantanes, respectively, and the RRF from 1-MD for quantitation of methyldiamantantes and other methylated diamantanes, respectively. Based on the dilution factor of samples and the determined results, the concentrations for each target analyte were calculated (Table 7).…”

“…To simplify, however, relative response factors (RRF) of each diamondoid to the corresponding internal standards were generally assumed to be one. In addition, the relative response factors of a diamondoid kit (including A, 1-MA, 2-MA, 1-EA, 2-EA, 1,3-DMA, 1-E-3-MA and 1,3,5-TMA) relative to deuterated n-alkanes (n-dodecane-d 26 and n-hexadecane-d 34 ) and five adamantanes (A, 1-MA, 2-MA, 2-EA, and 1,3-DMA) relative to the d 16 -adamantane have been used for quantification of diamondoids by GC-MS (Wang et al, 2006;Azevedo et al, 2008;Springer et al, 2010). In this study, calibration curves of response factors for ten diamondoid standards (i.e., A, 1-MA, 1,3-DMA, 1,3,5-TMA, 2-MA, 1-EA, 1-E-3-MA, 2-EA, D and 1-MD) were obtained by the GC-MS-MS and GC-MS analyses.…”

“…Since adamantane (the simplest diamondoid) was first discovered in petroleum in 1933, more diamondoids have been detected in many crude oils (Bender et al, 1986;Williams et al, 1986;Wingert, 1992;Chen et al, 1996;Dahl et al, 1999;Grice et al, 2000;Azevedo et al, 2008), petroleum products (Wang et al, 2006), coals and sedimentary rocks (Imuta and Ouchi, 1973;Aczel et al, 1979;Schulz et al, 2001;Wei et al, 2006a), and gas condensates (Lin and Wilk, 1995;Stout and Douglas, 2004;Sassen and Post, 2008). Furthermore, some higher diamondoids (more than three diamond cages) have been separated and identified from petroleum (Dahl et al, 2003).…”

“…Therefore, they have been widely used to determine the thermal maturity of highly mature crude oils (Chen et al, 1996;Li et al, 2000;Zhang et al, 2005), assess the extent of oil cracking (Dahl et al, 1999) and investigate the secondary alteration of crude oils, such as mixing, biodegradation and thermochemical sulfate reduction (TSR) (Dahl et al, 1999;Grice et al, 2000;Wei et al, 2007aWei et al, , 2011. Because of their stability and resistance to biodegradation, diamondoid hydrocarbons have also been utilized to identify the sources of oil spills (Stout and Douglas, 2004;Wang et al, 2006).…”

“…For example, methyldiamantane concentration (4-+ 3-methyldiamantane) can be used to estimate the extent of oil cracking (Dahl et al, 1999) and the relative abundance of diamondoids in light petroleum and gas condensates is an important ''fingerprinting'' tool to identify the sources of oil spills (Stout and Douglas, 2004). Although diamondoids occur in almost all crude oils and in most petroleum products (Wang et al, 2006), normal crude oils commonly contain very low concentrations, typically at the low ppm or even sub-ppm level (Fort and Schleyer, 1964;Wingert, 1992;Dahl et al, 1999;Wei et al, 2007a). Thus, a highly selective and sensitive detection method is required to quantify such trace components in normal crude oils and characterize their subtle variations.…”