## 1 Introduction  
The oil sands in Canada's northern Alberta region represent the third-largest proven oil reserve in the world. Oil sands production is expected to grow from 2.91 million barrels per day (bpd) in 2018 to 4.25 million bpd by 2035 [1]. Mining and processing of oil sands involves a hot water bitumen extraction process that results in the production of large volumes of oil sands process-affected water (OSPW) that contains a mixture of organic and inorganic compounds. These compounds include salts, trace metals, BTEX (benzene, toluene, ethylbenzene, and xylene), polyaromatic hydrocarbons (PAHs), and naphthenic acids (NAs) [2, 3]. NAs have been identified as a main contributor of OSPW toxicity [4, 5, 6, 7]. The molecular speciation of NAs using accurate mass spectrometry and high-resolution mass spectrometry is required to generate and confirm chemical formulae to effectively characterize the organic compounds and monitor their removal during remediation experiments. Additionally, off-line sample cleanup and liquid chromatography (LC) separations can help reduce variable ion suppression and improve quantitative evaluations of OSPW. There are three common classifications used to describe the organic chemical species in OSPW. The first are the classical NAs (cNAs) that have the general molecular formula \(\mathrm{C_{n}H_{2n+z}O_{2}}\) where \"n\" is the number of carbon atoms and \"z\" is either zero or a negative even integer representing the hydrogen deficiency resulting from saturated alicyclic ring structures (Figure 1) [8]. Each value of z = \(-\)2 represents an additional ring or double bond and is referred to as a double bond equivalent (DBE). The double bond found in the carboxylate moiety is included in references to DBE, but it is excluded when referencing the z-value of NAs. The second classification group is NAs that include O\({}_{3}\), O\({}_{4}\) and higher oxygenated species, and are referred to as oxy-NAs. While cNAs are the most abundant species in freshly produced OSPW, relatively high abundances of O\({}_{3}\) and O\({}_{4}\) species may also be present in OSPW and may be temporal indicators of transformations. Naphthenic acid fraction compounds (NAFCs) are the third general classification group and is a broad, all-inclusive definition of OSPW organics. NAFCs are the acid extractable organics that include cNAs, oxy-NAs, and compounds with aromatic rings, unsaturated groups, nitrogen, and/or sulphur atoms [9]. Common chemical species identified in NAFCs include SO\({}_{2}\), SO\({}_{3}\) and various NO-containing compounds. Effective OSPW detoxification strategies [10; 11; 12; 13; 14; 15] rely on a thorough understanding of the organic compounds that contribute to toxicity [5; 7]. Mass spectrometry (MS) is the most common method of detection for organic compounds in OSPW, with the simplest and least expensive approach being unit mass resolution quadrupole MS. Quadrupoles with unit mass resolution have limited applications due to low resolution. For example, such instruments cannot differentiate between the masses at 32 amu arising from either two oxygens (2 \(\times\) 16 amu = 32 amu) and a single sulfur (32 amu) in a given ion. The complexity of OSPW components can be better determined using high-resolution accurate mass (HRAM) instruments. Fourier transform ion cyclotron resonance (FT-ICR), Orbitrap, and time-of-flight (TOF) mass spectrometers are capable of mass accuracies of four or more decimal points. This resolution is sufficient to determine or confirm molecular formulae in the mass range that is typical of NAs and able to speciate elemental composition (e.g., O\({}_{2}\) = 31.9898; S = 31.9721). A previous review article [16] evaluated eight areas for consideration in designing a \"semi-quantitation\" approach to MS analysis of NAFCs in OSPW (Table 1). Semi-quantitative methods do not have authentic reference standards available for all target compounds. Therefore, they use the response factors of structurally similar compounds to estimate concentrations.