A traceable reference for direct comparative assessment of total naphthenic acid concentrations in commercial and acid extractable organic mixtures derived from oil sands process water

ABSTRACT

The advantage of using naphthenic acid (NA) mixtures for the determination of total NA lies in their chemical characteristics and identification of retention times distinct from isobaric interferences. However, the differing homolog profiles and unknown chemical structures of NA mixtures do not allow them to be considered a traceable reference material. The current study provides a new tool for the comparative assessment of different NA mixtures by direct reference to a single, well-defined and traceable compound, decanoic-d₁₉ acid. The method employed an established liquid chromatography time-of-flight mass spectrometry (LC/QToF) procedure that was applicable both to the classic O2 NA species dominating commercial mixtures and additionally to the O4 species known to be present in acid extractable organics (AEOs) derived from oil sands process water (OSPW). Four different commercial NA mixtures and one OSPW-derived AEOs mixture were comparatively assessed. Results showed significant difference among Merichem Technical, Aldrich, Acros, and Kodak commercial NA mixtures with respect to “equivalent to decanoic-d₁₉ acid” concentration ratios to nominal. Furthermore, different lot numbers of single commercial NA mixtures were found to be inconsistent with respect to their homolog content by percent response. Differences in the observed homolog content varied significantly, particularly at the lower (n = 9–14) and higher (n = 20–23) carbon number ranges. Results highlighted the problem between using NA mixtures from different sources and different lot numbers but offered a solution to the problem from a concentration perspective. It is anticipated that this tool may be utilized in review of historical data in addition to future studies, such as the study of OSPW derived acid extractable organics (AEOs) and fractions employed during toxicological studies.

KEYWORDS:

• Commercial lots
• concentration
• estrogens
• fatty acids
• homologs
• Naphthenic
• OSPW
• QToF
• resin acids

Acknowledgments

The authors' gratefully acknowledge the support and input of their colleagues, notably Liane Chow, Ceara MacInnis, Lauretta Liem, and Norman Berke of the Pacific Environmental Science Centre of Environment & Climate Change Canada, North Vancouver, B. C. Appreciation is extended to Dr. John Headley (Environment & Climate Change Canada, Saskatoon) and Harold Malle (Environment & Climate Change Canada, Burlington) for helpful discussion. They further gratefully acknowledge and appreciate the goodwill of Syncrude Canada Ltd. for providing Environment & Climate Change Canada with original OSPW samples.