Direct mass spectrometric analysis of naphthenic acids and polycyclic aromatic hydrocarbons in waters impacted by diluted bitumen and conventional crude oil

Abstract

Crude oil spills have well-documented, deleterious impacts on the hydrosphere. In addition to macroscopic effects on wildlife and waterscapes, several classes of petroleum derived compounds, such as naphthenic acids (NAs) and polycyclic aromatic hydrocarbons (PAHs), may be released into the water and present aquatic contamination hazards. The concentrations of these contaminants may be affected by both oil type and water chemistry. We characterize the concentrations of NAs and PAHs in natural and constructed waters, spanning a range of pH and salinity, and directly compare the influence of diluted bitumen (DB) and conventional crude (CC) oil, using condensed-phase membrane introduction mass spectrometry (CP-MIMS) as a direct sampling, on-line technique. The concentration and isomer class profiles of classical NAs in the aqueous phase were assessed using electrospray ionization in negative-ion mode as [M-H]− whereas PAH concentrations were monitored using liquid electron ionization (LEI) in positive-ion mode as [M+•]. NA concentrations (0.03–25 ppm) were highly pH-dependent, and an order of magnitude greater in water samples contaminated with DB than CC. Conversely, concentrations of naphthalene (10–130 ppb) and alkyl-naphthalenes (10–90 ppb) were three to four-fold higher in water samples exposed to CC. We demonstrate that naturally occurring dissolved organic matter does not bias results from the membrane sampling approach employed, and that DB and CC contaminated waters can be differentiated using principal component analysis of the NA isomer class distribution in both constructed and natural waters. Finally, we describe the first demonstration of the concurrent analysis of trace NAs and PAHs in the same water sample by controlling perm-selectivity at the membrane and the ionization mode of the mass spectrometer. The techniques employed here for trace analysis of petroleum derived compounds in water can be applied to rapid screening and real-time monitoring of contamination and remediation processes.