6020 r2009 American Chemical Society pubs.acs.org/EF Energy Fuels 2009, 23, 6020–6025 : DOI:10.1021/ef9007104 Published on Web 11/11/2009 Application of Superheated Water Extraction in Geochemical Evaluation of Source Rocks Akinsehinwa Akinlua* ,† and Roger M. Smith ‡ † Fossil Fuel and Environmental Research Group, Department of Chemistry, Obafemi Awolowo University, Ile-Ife, Nigeria and ‡ Department of Chemistry, Loughborough University, Loughborough LE11 3TU, United Kingdom Received July 14, 2009. Revised Manuscript Received October 26, 2009 Application of superheated water was investigated for the extraction of organic compounds of petroleum exploration importance. Using Niger Delta samples as a case study, the geochemical ratios and parameters were calculated from n-alkane and isoprenoid hydrocarbon data. The pristane/phytane, pristane/nC 17 , Ph/ nC 18 ratios and carbon preference index (CPI) ranged from 0.90 to 1.29, 0.61 to 2.30, 0.86 to 1.44, and 0.88 to 1.88 for the western Niger Delta samples, respectively, and from 0.35 to 3.49, 1.01 to 3.03, 0.87 to 1.98, and 1.00 to 2.15 for the eastern Niger Delta samples, respectively. The geochemical plots revealed that a preponderance of the samples from both western and eastern Niger Delta had mixed organic matter input and a good number of the samples also had contributions from terrestrial organic matter, while few samples had strong contributions from marine organic matter. The plots also indicated that the samples were sourced by organic matter deposited in more reducing environments than oxidizing environments. There was no significant difference in geochemical characteristics between western Niger Delta samples and eastern Niger Delta samples. Biomarker data also confirmed that the samples are mainly of terrestrial and mixed organic matter origin. The results of this study agreed with the results of previous studies based on Soxhlet extraction sample preparation. The results obtained from Soxhlet extraction of the same set of samples were comparable to those of superheated water extraction. The study showed that superheated water extraction provides a better alternative to Soxhlet extraction as the sample preparation procedure in geochemical evaluation of petroleum source rocks because of its environmentally friendly nature. 1. Introduction In petroleum exploration, source rock studies are an im- portant component of the evaluation of petroleum potential of any sedimentary basin. Organic compounds in the source rocks constitute invaluable tools to understand the quality of petroleum source rocks. Compounds of particular impor- tance include n-alkanes, isoprenoid alicylic hydrocarbons, terpanes, steranes, etc. These compounds are useful to deter- mine the origin, depositional environments, thermal maturity, and in some cases, the age of the organic matter. 1-8 These compounds are traditionally obtained from the rock matrix by Soxhlet extraction with organic solvents prior to instrumental analysis. These organic solvents are toxic and environmentally unfriendly, which has led to the quest for benign green analytical extraction techniques. One of such techniques is supercritical fluid extraction (SFE) with carbon dioxide, which as been successfully applied to the extraction of organic compounds of petroleum exploration importance from source rocks. 9-14 However, the SFE instrumentation required is relatively expensive. Hence, there is still a need for an alternative method that will be cheaper and equally environmentally friendly, and in recent years, superheated water extraction (SWE) has been shown to provide such an alternative. SWE has been applied to the extraction of organics from solid environmental samples, such as soil and sediments, 15-18 *To whom correspondence should be addressed. E-mail: aakinlua@ oauife.edu.ng. (1) Bray, E. E.; Evans, E. D. Geochim. Cosmochim. Acta 1961, 22, 2–15. (2) Meyers, P. A. Org. Geochem. 1997, 27, 213–250. (3) Obaje, N. G. NAPE Bull. 2000, 15, 29–45. (4) Peters, K. E.; Snedden, J. W.; Sulaeman, A.; Sarg, J. F.; Enrico, R. J. AAPG Bull. 2000, 84, 12–44. (5) Nytoft, H. P.; Bojesen-Koefoed, J. A. Org. Geochem. 2001, 32, 841–856. (6) Banerjee, A.; Pahari, S.; Jha, M.; Sinha, A. K.; Jain, A. K.; Kumar, N.; Thomas, N. J.; Misra, K. N.; Chandra, K. AAPG Bull. 2002, 86, 433– 456. (7) Hanson, A. D.; Ritts, B. D.; Moldowan, J. M. AAPG Bull. 2007, 91, 1273–1293. (8) Alsharhan, A. S.; Abd El-Gawad, E. A. J. Pet. Geol. 2008, 3, 191– 212. (9) Monin, J. C.; Barth, D.; Perrut, M.; Espitalie, M.; Durand, B. Org. Geochem. 1998, 13, 1079–1086. (10) Hopfgartner, G.; Veuthey, J. L.; Gulac-ar, F. O; Buchs, A. Org. Geochem. 1990, 15, 397–402. (11) Greibrokk, T.; Kadke, M.; Skurdal, M.; Willsch, H. Org. Geo- chem. 1992, 18, 447–455. (12) Jaffe, R.; Diaz, D.; Hajje, N.; Chen, L.; Eckardt, C.; Furton, K. G. Org. Geochem. 1997, 26, 59–65. (13) Furton, K. G.; Chena, L.; Jaffe, R. J. J. High Resolut. Chroma- togr. 1999, 22, 623–627. (14) Akinlua, A.; Torto, N.; Ajayi, T. R. J. Supercrit. Fluids 2008, 45, 57–63. (15) Di Corcia, A.; Caracciolo, A. B.; Crescenzi, C.; Guiliano, G.; Murtas, S.; Samperi, R. Environ. Sci. Technol. 1999, 33, 3271–3277. (16) Hawthorne, S. B.; Trembley, S.; Moniot, C. L.; Grabanski, C. B.; Miller, D. J. J. Chromatogr., A 2000, 886, 237–244. (17) Krieger, M. S.; Wynn, J. S.; Yoder, R. N. J. Chromatogr., A 2000, 897, 405–413. (18) Chienthavorn, O.; Su-in, P. Anal. Bioanal. Chem. 2006, 385, 83– 89. (19) Hawthorne, S. B.; Yang, Y.; Miller, D. J. Anal. Chem. 1994, 66, 2912–2920. (20) Kipp, S.; Peyrer, H.; Kleibohmer, W. Talanta 1998, 46, 385–393. (21) Young, T. E.; Ecker, S. T.; Synovec, R. E.; Hawley, N. T.; Lomber, J. P.; Wai, C. N. Talanta 1998, 45, 1189–1199.