Gas chromatographic fingerprinting of crude oil from ... - Springer Link

Environ Monit Assess (2008) 141:359–364 DOI 10.1007/s10661-007-9902-0

Gas chromatographic fingerprinting of crude oil from Idu-Ekpeye oil spillage site in Niger-delta, Nigeria Inimfon A. Udoetok & Leo C. Osuji

Received: 16 November 2006 / Accepted: 27 August 2007 / Published online: 4 October 2007 # Springer Science + Business Media B.V. 2007

Abstract Samples were collected from an oil polluted site in Niger-delta, Nigeria. Gas chromatographic analyses carried out on the samples revealed an abundance of n-alkanes within the n-C8–n-C23 region. The pristane/phytane ratio of 5.70 obtained for the samples depicted a plant/terrestrial source input and a possible oxic depositional environment. The n-C17/ pristane and n-C18/phytane ratios of 2.80 and 2.77, respectively, suggested that the spilled oil was only slightly weathered, as corroborated by the presence of peaks in the aromatic hydrocarbon fingerprints. The polycyclic aromatic hydrocarbon (PAH) fractions showed that the hydrocarbon fractions might have undergone combustion and/or that there was bush burning at the site prior to the oil spill incidence. This is supported by the abundance of high-molecularweight PAHs which are pyrogenic in nature. High molecular weight PAHs are products of the combustion of petroleum or its products. The phenanthrene/ anthracene ratio of 0.95, fluorathene/pyrene ratio of 2.23 and the ∑ (other three to six ringed PAHs)/∑ (five I. A. Udoetok (*) Akwa Ibom State University of Technology, University Town, P. M. B. 1167 Uyo, Akwa Ibom State, Nigeria e-mail: [email protected] L. C. Osuji Department of Industrial and Pure Chemistry, University of Port Harcourt, PMB 5323 Choba, Port Harcourt, Nigeria e-mail: [email protected]

alkylated PAHs) ratio far greater than unity (4.10) also affirm this. On the other hand, the benzo (a) anthracene to chrysene ratio of 0.24 confirms the petrogenic origin of the spilled oil because chrysene which is highly abundant is a fossil PAH. Keywords Pristane . Phytane . Oxic . PAH . Petrogenic . Pyrogenic . Fingerprints

Introduction Petroleum is a complex mixture that contains thousands of different organic compounds. Successful oil fingerprinting involves appropriate sampling, analytical approaches and data interpretation strategies. A wide variety of instrumental and non-instrumental techniques are currently used in the analysis of oil hydrocarbons, which include gas chromatography (GC), gas chromatography–mass spectrometry (GC– MS), high performance liquid chromatography (HPLC), thin layer chromatography (TLC), and ultraviolet (UV) spectroscopy etc. (Wang and Fingas 2003). Of all these techniques, GC techniques are the most widely used. Compared to other techniques, GC methods have now been enhanced by more sophisticated analytical techniques, which make it capable of analyzing oil specific biomarker compounds and polycyclic aromatic hydrocarbons. The accuracy and precision of analytical data has been improved and optimized by a series of quality assurance/quality control measures, and the laboratory

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Environ Monit Assess (2008) 141:359–364

of low-molecular-weight hydrocarbons from the chromatograms first, due to their preferential consumption by the microorganisms provide adequate information on the changes taking place during the degradation process (Udoetok 2005). The trend developed as a result of the disappearance of these hydrocarbon fractions from the chromatograms can then be employed in oil spilled source identification as no two oils will exhibit the same fingerprints. This is observed on comparing Figs. 1 and 2. This research therefore explores the usefulness of the gas chromatographic fingerprinting technique as a veritable ‘tool’ for oil spill source identification, evaluation of origin of oil, and biodegradation. Materials and methods Site description The study site is located at Idu-Ekpeye in Ahoada West Local Government Area of Rivers State, Fig. 1 Chromatogram showing BTEX fingerprints of the sample

data handling capability has been increased through advances in computer technology. Several reviews have been published on the analytical methodologies for characterization and identification of oil hydrocarbons using various analytical techniques (Kaplan and Galperon 1996; Wang et al. 1999; Stout et al. 2002). The gas chromatographic fingerprinting technique requires using a gas chromatograph in analyzing the spilled crude oil for hydrocarbon fractions (total petroleum hydrocarbon (TPH), benzene, toluene, ethyl benzene and xylene (BTEX), polycyclic aromatic hydrocarbons (PAH) present in the oil. A chromatogram which is obtained on completion of the analysis shows the components of the analyzed oil and these components can be used in calculating various ratios. These ratios are used for the evaluation of parameters such as maturity, source and biodegradation of the oil. Since oil fingerprinting shows a representation of the relative concentration of compounds present in the analyzed oil, the total petroleum hydrocarbon (TPH) content (a term used to describe a large family of several hundred chemical compounds present in crude oil) of the spilled crude oil will be obtained through this technique. Also, the degradation process as depicted by the trend in the disappearance

Fig. 2 Chromatogram of an unweathered crude oil

Environ Monit Assess (2008) 141:359–364 Table 1 Total petroleum hydrocarbon (TPH) content of samples Total petroleum hydrocarbon Hydrocarbon fraction

Amount (mean ± SE mg/kg)

C8 C9 C10 C11 C12 C13 C14 C15 C16 C17 Pristane C18 Phytane C19 C20 C21 C22 C23

385.83±425.19 346.92±200.82 117.12±119.13 125.00±226.84 726.05±409.58 3,946.58±2,711.99 1,179.40±1,114.16 1,172.18±2,711.99 675.92±239.64 1,851.45±1,771.43 662.71±750.10 322.90±329.49 116.37±101.05 77.64±94.11 89.37±65.87 105.30±151.74 255.32±372.05 404.08±750.09

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operational conditions; flow rate (H2 30 ml/min, air 300 ml min and N2 30 ml/min); injection temperature (50°C), detector temperature (320°C); recorders’ voltage (IMV); and chart speed 1cm/min. For interpretation of results, the GC recorder was interfaced to a Hewlett Parker (hp) Computer (6207AA Software, Kayak XA PIT/350 W/48 megabytes CD-ROM). The chromatograms were quantified with respect to the internal standards.

Results and discussion TPH (n-alkanes), PAH and BTEX Total petroleum hydrocarbon (TPH) content is a term used to describe a large family of several hundred chemical compounds present in crude oil. The n-alkane components of the analyzed oil showed a distribution of paraffins from n-C8 to n-C23 with the fractions n-C8, n-C9, n-C12, n-C13, n-C14, n-C15, n-C16, n-C18, pristane and n-C23 showing relatively high concentrations (Table 1, Fig. 3). Highly weath-

Nigeria. It is found between longitude 6°25′–6°35′E and latitude 4°45′–5°10′N. The oil spillage occurred in April 2005 and the post impact period was only one week. Field reconnaissance and sampling design Sampling was carried out as part of field reconnaissance survey. Sampling plots were erected at the spill site. A sampling area of 200×200 m was divided into 100 grid plots, each measuring 20×20 m, and 30% of this (i.e. 33 grid plots) were randomly selected, and soils were taken from three replicate quadrates. Soil samples were collected at surface (0–15 cm) and subsurface (15–30 cm) depths. The soil samples were put in aluminium foil bags and labeled accordingly. Oil extraction and chromatographic analysis Five grams (5 g) of homogenized soil samples were accurately weighed into clean, dry beakers. The weighed samples were extracted with 10 ml of hexane respectively and passed through a filter paper. The extract (the hydrocarbon/hexane mix), now ready for gas chromatography, was injected into a Varian model 3400 gas chromatograph (GC) with the following

Fig. 3 Chromatogram showing aliphatic hydrocarbon fingerprints of the sample

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ered oils show significant losses in the low-molecularweight n-alkanes and as a result, the ratio n-C17/ pristane and n-C18/phytane tends to be in the same range as those measured for the source oil. Therefore, for fresh or mildly weathered oil products, alkanes and isoprenoid analysis may be used for oil source identification. In heavily weathered oils, the n-alkanes, and even the isoprenoids in some cases may be completely lost (Osuji et al. 2006). Therefore a ratio of 2.80 and 2.77 for n-C17/pristane and n-C18/phytane respectively obtained for the sample suggest that the released oil was only slightly weathered as at the time of sample collection. A value of 5.70 was obtained for the pristane/phytane ratio. This ratio can be a useful source index of spilled-oil’s depositional environment. Since pristane represents a product of decarboxylation, the ratio pristane/phytane (Pr/Ph) tends to be high in oxidizing environments (Hunt 1996). Thus the Pr/Ph ratio of 5.70 for this sample implies an oxic depositional environment for the spilled oil. The samples also showed a distribution pattern of odd carbon-numbered alkanes being much abundant than even-numbered alkanes in the lower alkane range, resulting in a high carbon preference index (CPI) values which is defined as the ratio of the sum of the odd carbon-numbered alkanes to the ratio of the even carbon-numbered alkanes. The CPI value for the spilled oil was approximately 2.0 for the lower alkane range, thus suggesting that the spilled oil might have been derived from a plant/terrestrial source input. On the whole, the CPI and the Pr/Ph ratio for this sample points to an oxic depositional environment and a phytoplankton source input. This therefore shows that fingerprinting technique can be used to trace the origin of any oil, weathered or unweathered. In some cases, qualitative chemical analysis and visual comparison of chromatograms of spilled oil, suspected candidate sources and background materials may sufficiently meet the needs of a forensic investigation, since no two oils have the same fingerprints. However, when the chemical similarly difference between the spilled oil and the suspected sources is not obvious, or a large number of candidate sources are involved, or the spilled oil has undergone heavy weathering and significant alteration in its chemical compositions, the qualitative approach would be difficult to defend, and therefore a quantitative fingerprinting analysis of degradation-resistant and biomarker compounds must be performed (Wang et al. 1999).


Crude oils and refined products from different sources can have different polycyclic aromatic hydrocarbon (PAH) distributions. Also, many PAH compounds are more resistant to weathering than their saturated hydrocarbon counterparts (n-alkanes and isoprenoids) and volatile alkyl benzene compounds, thus making PAHs one of the most valuable fingerprinting classes of hydrocarbons for oil identification. Even differences between the same type of products are discernable through examination of the PAH distribution. PAH compounds can be grouped into two viz: Alkylated homologous PAHs which include naphthalene, phenanthrene, dibenzothiophenes, fluorene and chrysene, and other EPA priority PAHs which include acenaphthalene, acenaphthene, anthracene and pyrene etc. The PAH distribution of the sample for this study (Table 2, Fig. 4) showed low values for two-ringed PAHs (alkylated homologues) such as naphthalene, and very high values for three to six ringed PAHs (EPA priority PAHs) such as pyrene, anthrcene and acenaphthalene etc. These high molecular weight PAHs (three to six ringed PAHs) are known as pyrolytic PAHs while the low molecular weight PAHs (two-ringed PAHs) are known as fossil PAHs (Cinta

Table 2 Polycyclicaromatic hydrocarbon (PAH) content of samples Polycyclicaromatic hydrocarbon Hydrocarbon fraction


Naphthalene Acenaphthylene Acenaphthene Fluorene Phenanthrene Anthracene Fluoranthene Pyrene Benzo(a) anthracene Chrysene Benzo (b) fluoranthene Benzo (k) fluoranthene Benzo (a) Pyrene Indo 1,2,3 cd Pyrene Dibenzo (a,b) anthracene Benzo (ghi) perylene

8.16±6.3 69.15±48 88.58±31.66 126.25±46.73 151.1±65.27 158.64±47.26 281.96±145.85 126.26±381.63 313.09±351.86 269.31±191.18 355.48±333.27 134.23±63.9 63.9±310.96 375.81±287.31 73.66±24.85 231.37±192.87


Fig. 4 One of the fingerprints showing PAH fractions of the sample

et al. 2000). The abundance of the high-molecularweight PAHs suggest that though these hydrocarbon fractions were released from a spilled oil (petrogenic source meaning from petroleum), they might have undergone combustion and/or there might been an incidence of bush burning before the spillage, since high molecular weight PAHs are products of the combustion of petroleum or its products (Bence et al. 1996; Bjǿeseth 1985; Page et al. 1996) This is supported by the phenanthrene/anthracene and fluorathene/ pyrene ratios being less than 10 (1) respectively because both anthracene and fluorathene are pyrolytic PAHs (product of pyrolysis) [12]. Also, the ratio of the sum of other three to six ringed PAHs (∑ other three to six ringed PAHs) to the sum of five alkylated PAHs (∑ five alkylated PAHs) which is suppose to be less than 0.01 for petrogenic PAHs is far greater than unity (4.10). This also supports the combustion of the hydrocarbons. On the other hand, the ratio of benzo (a) anthracene to chrysene which is suppose to be above unity for PAHs from pyrogenic source (PAHs produced as a result of the pyrolysis) was below unity showing that

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chrysene was abundant. This affirms that though the combustion of the hydrocarbons after the spill and/or the burning of the farmland prior to the spill might have led to the abundance of the pyrogenic PAHs, the PAHs were originally of petrogenic origin after all. Studies such as that of Benlahcen et al. 1997 have shown that there are significant differences between ratios such as ∑ (other three to six ringed PAHs)/∑ (five alkylated PAHs) and phenanthrene/anthracene for petrogenic and pyrogenic PAHs. They show great consistency from sample to sample and are subject to little interference from the concentration fluctuation of individuals within the PAH series. The fingerprints of the aromatic components of the spilled oil are shown in Table 3, Fig. 1. The primary components of the aromatic hydrocarbon are the benzene, toluene, ethyl benzene and xylene (BTEX). The result of this study shows that there were peaks in the BTEX fingerprints thus signifying that the spilled oil was still fresh on site. These aromatic hydrocarbons are of limited importance in fingerprinting studies due to their high volatility. However, Kaplan and Galperon (1996) used these hydrocarbon fractions to determine whether an oil spill is recent or not. They gave the formula for release time as Rb=(B+T)/ (E+X), where Rb=release time, B=Benzene, T= Toluene, E=Ethylbenzene, and X=Xylene and a range of 1.5 and 6.0 for Rb to mean a recent release of oil to environment. Based on these, a value of 1.53 for Rb confirms that at the time of sampling, the spilled oil was still fresh on site.

Table 3 Benzene, toluene, ethyl benzene, and xylene (BTEX) content samples BTEX Hydrocarbon fraction


Benzene Chlorobenzene 1,2, dichlorobenzene 1,3, dichlorobenzene 1,4, dichlorobenzene Ethyl benzene Toluene m,p-Xylene O-Xylene

27.08±23.04 16.76±14.06 20.08±8.96 29.05±28.01 5.23±2.26 12.06±5.91 19.44±12.1 18.25±8.75 3.66±3.23

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Conclusions The gas chromatographic fingerprinting technique involves using a gas chromatograph for analyses. The advances in this technique and data interpretation methods and approaches in recent years have now allowed for detailed qualitative and quantitative characterization of spilled oils and subsequent source identification. It is a veritable tool for oil spill source identification and differentiation, when employed adequately. However, in many cases, particularly for complex hydrocarbon mixtures or extensively weathered and degraded oils, there is no single fingerprinting technique which can meet the objectives of oil spill source identification and quantitatively allocate hydrocarbons to their respective sources. Therefore, combined and integrated multiple tools are often necessary under this situations. Developments in fingerprinting techniques will continue as analytical and statistical methods are developed. Hence it is believed that in the nearest future, these developments will further make gas chromatographic fingerprinting technique, a veritable tool for oil spill source identification and differentiation. Acknowledgements The authors are grateful to the department of petroleum resources (DPR) for permissions granted and Shell Petroleum Development Company of Nigeria (SPDC) for providing unclassified data and laboratory space, the Preparatory Chemistry (PC) laboratory. Mr. Adolphus Azubuike is also acknowledged for facilitating this work.

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