Identification of individual tetra‐ and pentacyclic naphthenic acids in oil sands process water by comprehensive two‐dimensional gas chromatography/mass spectrometry

Abstract

The oils sands industry of Canada produces large volumes of process water (OSPW) which is stored in large lagoons. The OSPW contains complex mixtures of somewhat toxic, water-soluble, acid-extractable organic matter sometimes called 'naphthenic acids' (NA). Concerns have been raised over the possible environmental impacts of leakage of OSPW and a need has therefore arisen for better characterisation of the NA. Recently, we reported the first identification of numerous individual tricyclic NA in OSPW by comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry (GCxGC/ToF-MS) of the methyl esters. The acids were diamondoid adamantane acids, resulting, it was proposed, from biotransformation of the corresponding alkyladamantane hydrocarbons, which is a known process. Biotransformation of higher alkylated diamondoid hydrocarbons was, until now, unknown but here we describe the identification of numerous pentacyclic NA as diamantane and alkyldiamantane acids, using the same methods. Further, we suggest tentative structures for some of the tetracyclic acids formed, we propose, by ring-opening of alkyldiamantanes. We suggest that this is further evidence that some of the acid-extractable organic matter in the OSPW originates from extensive biodegradation of the oil, whether in-reservoir or environmental, although other oxidative routes (e.g. processing) may also be possible. The results may be important for helping to better focus reclamation and remediation strategies for NA and for facilitating the identification of the sources of NA in contaminated environmental samples.

Toxicity of naphthenic acid fraction components extracted from fresh and aged oil sands process-affected waters, and commercial naphthenic acid mixtures, to fathead minnow (Pimephales promelas) embryos

“…Commercial NA mixtures had greater proportions of structurally simple O 2 acid species (i.e., Z = 0; acyclic), while all NAFC extracts from OSPW had proportionally greater quantities of more complex O 2 species, alicyclic and/or aromatic rings (especially Z = −4 and −6) and very few acyclic compounds. Such composition data are in general agreement with previously published analyses of other commercial NA mixtures (Rowland et al, 2011d;Rudzinski et al, 2002), NAFC extracts and OSPW (Grewer et al, 2010;Headley et al, 2013a,b;Holowenko et al, 2002;Rowland et al, 2011c;Scarlett et al, 2013). Our toxicity data also support previous observations that NA and NAFC mixtures with higher proportions of smaller, simpler acids (e.g., commercial NAs) are more toxic than those with proportionately more complex acids (e.g., NAFC extracts; Clemente et al, 2004;Holowenko et al, 2002;Johnson et al, 2010).…”

Synthesis and mass spectrometry of some tri‐and tetracyclic naphthenic acids

“…3(F) and 3(G)) contained several of the features of the spectrum of a component assigned previously in the acidic extract of oil sands process-affected water as the methyl ester of tetracyclo-[7.3.1.0 2,7 .0 6,11 ]tridecane carboxylic acid (viz: m/z 234, 201, 175 [3] ) but with somewhat different ion intensities. The GCxGC retention times were also fairly close (within 1-2 min GC1) to those of the tentatively identified substituted and unsubstituted tetracyclo [7.3.1.0 2,7 .0 6,11 ]tridecane carboxylic acids (methyl ester), indicating that the previous assignments [3] may be correct, but no evidence for the presence of the specific tetracyclotridecane-12-carboxylic acid isomers synthesised herein could be found in the methyl esters of the only sample of oil sands process-affected water acid extractables currently available to us.…”

“…[8] The alcohol was oxidised to adamantane-2-carboxylic acid (IV). [9] The methyl ester was prepared by heating the crude product with BF 3 [11] and the methyl esters by heating with BF 3 /methanol.…”

Trace analysis of total naphthenic acids in aqueous environmental matrices by liquid chromatography/mass spectrometry-quadrupole time of flight mass spectrometry direct injection

“…Derivatization procedures may alternately be biased toward acyclic and monocyclic groups over the polyoxy acid. Since polyoxy acids are known to increase during aging of oil sands process water, their monitoring in environmental samples is critical [5,6,11,15,30].…”

“…In this regard, quadrupole time of flight mass spectrometry (QToF), Orbitrap, and Fourier transform ion cyclotron resonance (FTICR) have been applied to the analysis of OSPW, although their application to routine quantitative monitoring has yet to be fully demonstrated [6]. In addition to high mass resolution applications, recent progress has been reported on the identification of several new classes of NAs (diamondoid adamantanes, diamantanes, monoaromatic acids) using comprehensive two dimensional GC/GC-ToF/MS by Rowland et al [14,15]. More recently, differential ion mobility spectrometry in combination with quadrupole time of flight mass spectrometry [16] and supercritical fluid/Orbitrap mass spectrometry [17] have also been employed by other authors for NA fingerprinting.…”