Sample preparation and high-resolution MS analysis of NAFCs

Water samples were extracted using an ENV + solid-phase extraction (SPE) method, as has been previously described by Headley et al. (2002). SPE cartridges were rinsed with 6 mL of Milli-Q water, 6 mL of LC–MS grade methanol (Fisher Scientific, Hampton NH, USA), and conditioned with a further 6 mL of Milli-Q water prior to sampling. Sample aliquots were measured to 100 mL and acidified to pH < 2 with formic acid. Acidified samples were drawn through prepared cartridges at 1–2 mL/min under vacuum conditions, rinsed with 6 mL of Milli-Q water to desalt, and then dried under gentle vacuum. Sample extracts were eluted with 6 mL of LC–MS grade methanol then evaporated at 40 °C under a gentle flow of 5.0-grade ultrahigh purity N₂ (Linde Canada, Saskatoon, SK). Dried sample eluents were reconstituted into 1 mL of 50:50 ACN:H₂O with 0.1% NH₄OH, then transferred to clean and labeled 2.0 mL LC–MS vials. Sample extracts were analyzed via loop injection to an LTQ Orbitrap Velos Elite™ mass spectrometer (Thermo Fisher Scientific, Waltham, MA) operating at 240,000 resolution (measured at 400 m/z) in negative ion electrospray ionization mode, as was previously described in the literature by Headley et al. (2011a). Concentrations of NAFCs were determined using a 5-point external standard calibration of Athabasca oil sands OSPW-derived NAFCs at known concentrations as described elsewhere (Ahad et al., 2020).