A statistical comparison of naphthenic acids characterized by gas chromatography–mass spectrometry Joyce S. Clemente a , N.G.N. Prasad b , Michael D. MacKinnon c , Phillip M. Fedorak a, * a DepartmentofBiologicalSciences,UniversityofAlberta,Edmonton,AB,CanadaT6G2E9 b DepartmentofMathematicalandStatisticalSciences,UniversityofAlberta,Edmonton,AB,CanadaT6G2G1 c SyncrudeCanadaLtd.,EdmontonResearchCentre,9421-17Avenue,Edmonton,AB,CanadaT6N1H4 Received 16 July 2002; received in revised form 1 November 2002; accepted 4 November 2002 Abstract Naphthenic acids are complex mixtures of alkyl-substituted acyclic and cycloaliphatic carboxylic acids, with the general chemical formula C n H 2nþz O 2 ,where n isthecarbonnumberand Z specifies a homologous family. These acids have a variety of commercial uses, including being used as wood preservatives. They are found in conventional and heavy oils, and in the oil sands of northeastern Alberta, Canada. Naphthenic acids are major contributors to the toxicity of tailings waters that result from the oil sands extraction process. Eight naphthenic acids preparations (four from commercial sources and four from the oil sands operations) were derivatized and analyzed by gas chromato- graphy–mass spectrometry. The composition of each mixture was summarized as a three-dimensional plot of the abundance of specific ions (corresponding to naphthenic acids) versus carbon number (ranging from 5 to 33) and Z family (ranging from 0 to )12). The data in these plots were divided into three groups according to carbon number (group 1 contained carbon numbers 5–14, group 2 contained carbon numbers 15–21, and group 3 contained carbon numbers 22–33). A t-test, using arcsine-transformed data, was applied to compare corresponding groups in samples from various sources. Results of the statistical analyses showed differences between various commercial naphthenic acids preparations, and between naphthenic acids from different oil sands ores and tailings ponds. This statistical approach can be applied to data collected by other mass spectrometry methods. Ó 2003 Elsevier Science Ltd. All rights reserved. Keywords: Naphthenic acids; Oil sands; t-test; Toxicity; Gas chromatography–mass spectrometry; Mass spectrometry 1. Introduction Naphthenic acids are found in many petroleums (Lochte and Littmann, 1955; Fan, 1991; Brient et al., 1995; Slavcheva et al., 1999; Jones et al., 2001). These relatively low molecular weight components (typically <500 Daltons) are readily dissolved as their carboxy- lates in water at neutral and alkaline pH. They are a complex mixture of alkyl-substituted acyclic and cyclo- aliphatic carboxylic acids with the general chemical formula C n H 2nþz O 2 , where n indicates the carbon num- berand Z iszerooranegative,evenintegerthatspecifies a homologous series. Fig. 1 shows examples of typical structures of naphthenic acids. The ring structures pre- dominantly contain 5- or 6-carbon atoms in various combinations.Naphthenicacidswithoneringbelongto the Z ¼2 family, those with two rings belong to the Z ¼4familyandsoon.Naphthenicacidsinthe Z ¼ 0 family are acyclic, but they are more likely to be Chemosphere 50 (2003) 1265–1274 www.elsevier.com/locate/chemosphere * Corresponding author. Tel.: +1-780-492-3670; fax: +1-780- 492-9234. E-mailaddress: phil.fedorak@ualberta.ca (P.M. Fedorak). 0045-6535/03/$ - see front matter Ó 2003 Elsevier Science Ltd. All rights reserved. PII:S0045-6535(02)00763-4