Positive and negative electrospray ionization analyses of the organic fractions in raw and oxidized oil sands process-affected water

• Oxidation processes transformed the distribution profiles of Ox, OxSy, and OxNy.
• Ozone was more effective than UV/H2O2 and ferrate (VI) in transforming the profiles.
• Positive mode Ox species were more oxygen-rich and more hydrogen-deficient.
• OxSy distribution was sensitive to the oxidation extent.
• Ox distribution detected by positive mode UPLC-TOF-MS should be used with caution.

This work investigated the oxidative transformation of the organic species in oil sands process-affected water (OSPW) using Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) and ultra-performance liquid chromatography time-of-flight mass spectrometry (UPLC-TOF-MS) in both negative and positive electrospray ionization (ESI) modes. This is the first time to apply FTICR-MS to investigate species transformation in OSPW treatments by ferrate (VI), UV/H2O2, and molecular ozone, and also this is the first preliminary study to use positive ESI to investigate organic species in addition to naphthenic acids (NAs) in these treatment processes. The oxidation processes with potassium ferrate (VI), UV/H2O2, and ozone transformed the distribution profiles of Ox, OxSy, and OxNy organic fractions (i.e., species containing oxygen, sulfur, and nitrogen, with x, y specifying the oxygen number and sulfur/nitrogen number, respectively), with OxSy distribution profiles showing the most sensitive responses to the oxidation extent and can be used as a signature fraction to evaluate the oxidation effectiveness. Negative mode UPLC-TOF-MS confirmed the transformation pattern of Ox species observed with FTICR-MS, but positive mode UPLC-TOF-MS results showed severe discrepancies with FTICR-MS results and should be subjected for future further investigation, regarding the relatively low mass resolution of UPLC-TOF-MS. The investigation of the transformation patterns of different organic species using two ionization modes was a preliminary study to enhance the understanding of the efficiency, selectivity, and mechanism of different oxidation processes in OSPW remediation for both NAs and non-NA species.

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