Characterization and Matching of Oil Samples Using Fluorescence Spectroscopy and Parallel Factor Analysis Jan H. Christensen,* ,†,‡,§ Asger B. Hansen, † John Mortensen, ‡ and Ole Andersen ‡ Department of Environmental Chemistry and Microbiology, National Environmental Research Institute, Frederiksborgvej 399, 4000 Roskilde, Denmark, Department of Life Sciences and Chemistry, Roskilde University, Universitesvej 1, 4000 Roskilde, Denmark, and Department of Natural Sciences, Royal Veterinary and Agricultural University, Thorvaldsensvej 40, 1870 Frederiksberg C, Denmark A novel approach for matching oil samples by fluores- cence spectroscopy combined with three-way decomposi- tion of spectra is presented. It offers an objective finger- printing based on the relative composition of polycyclic aromatic compounds (PACs) in oils. The method is complementary to GC-FID for initial screening of oil samples but can also be used for prescreening in the field, onboard ships, using a portable fluorescence spectrom- eter. Parallel factor analysis (PARAFAC) was applied to fluorescence excitation-emission matrixes (EEMs) of heavy fuel oils (HFOs), light fuel oils, lubricating oils, crude oils, unknown oils, and a sample collected in the spill area two weeks after the Baltic Carrier oil spill (Denmark, 2001). A total of 112 EEMs were decomposed into a five-factor PARAFAC model using excitation wave- lengths from 245 to 400 nm and emission wavelengths from 280 to 550 nm. The PARAFAC factors were com- pared to EEMs of PAC standards with two to five rings, and the comparisons indicate that each of the factors can be related to a mixture of PACs with similar fluorescence characteristics: a mixture of naphthalenes and diben- zothiophenes, fluorenes, phenanthrenes, chrysenes, and five-ring PACs, respectively. Oils were grouped in score plots according to oil type. Except for HFOs and crude oils, the method easily discriminated between the four oil types. Minor overlaps of HFOs and crude oils were observed along all five PARAFAC factors, and the vari- ability of crude oils was large along factor 2 due to a varying content of five-ring PACs. The spill sample was correctly assigned as a HFO with similar PAC pattern as oil from the cargo tank of the Baltic Carrier by compar- ing the correlation coefficient of scores for the oil spill sample and possible source oils (i.e., oils in the database). Accidental and deliberate oil spills occur frequently in the natural environment, and it can affect the ecosystem as well as human health due to the high content of toxic and mutagenic compounds in oil. Polycyclic aromatic compounds (PACs), which are present in high concentrations in oil, form a large group of relatively persistent compounds, several being carcinogenic, mutagenic, or both. Accordingly, the U.S. Environmental Protec- tion Agency (http://www.epa.gov) has classified 16 individual PACs as priority pollutants. In the Danish maritime territory, the frequency of minor oil spills (e.g., due to tank washings) was ∼400 year -1 during a 15- year period from 1987 to 2001, and worldwide the number of spills is enormous. Thus, there is a constant need for improving existing methods for oil characterization and identification in order to determine the source of spills. The standard method for chemical characterization of oil consists of initial screening using gas chromatography-flame ionization detection (GC-FID) followed by more comprehensive analyses by gas chromatography/mass spectrometry (GC/MS). 1,2 Numerous methods for chemical fingerprinting based on GC/ MS data exist, most of which basically compare the relative abundancies of selected petroleum hydrocarbons in spill samples and suspected sources. 1,3-7 However, initial screening of oil samples to reject obvious nonmatches from further analysis is also an important part of a multiple-criteria approach for oil spill identification, and it is often based on visual comparison of GC- FID chromatograms. 1 This method is subjective, time-consuming, and often limited mainly to the comparison of the n-alkane distribution, pristane/phytane ratio, and size and position of the unresolved complex mixture. Fluorescence spectroscopy is a screening method complemen- tary to GC-FID, since it focuses on a different part of the oil, namely, the PACs. 8-10 The fluorescence of individual PACs is * Corresponding author. Telephone: +45-35282366. Fax: +45-35282398. E-mail: jch@kvl.dk. † National Environmental Research Institute. ‡ Roskilde University. § Royal Veterinary and Agricultural University. (1) Daling, P. S.; Faksness, L. G.; Hansen, A. B.; Stout, S. A. Environ. Forensics 2002, 3, 263-78. (2) Wang, Z. D.; Fingas, M.; Page, D. S. J. Chromatogr., A 1999, 843, 369- 411. (3) Christensen, J. H.; Tomasi, G.; Hansen, A. B. Environ. Sci. Technol. 2005, 39, 255-60. (4) Christensen, J. H.; Hansen, A. B.; Tomasi, G.; Mortensen, J.; Andersen, O. Environ. Sci. Technol. 2004, 38, 2912-18. (5) Short, J. W. Environ. Forensics 2002, 3, 349-55. (6) Stout, S. A.; Uhler, A. D.; McCarthy, K. J. Environ. Forensics 2001, 2, 87- 98. (7) Wang, Z. D.; Fingas, M.; Sigouin, L. Environ. Forensics 2002, 3, 251-62. (8) Li, J. F.; Fuller, S.; Cattle, J.; Way, C. P.; Hibbert, D. B. Anal. Chim. Acta 2004, 514, 51-6. Anal. Chem. 2005, 77, 2210-2217 2210 Analytical Chemistry, Vol. 77, No. 7, April 1, 2005 10.1021/ac048213k CCC: $30.25 © 2005 American Chemical Society Published on Web 02/18/2005