Membrane Sampling Separates Naphthenic Acids from Biogenic Dissolved Organic Matter for Direct Analysis by Mass Spectrometry

Abstract

Oil sands process waters can release toxic naphthenic acids (NAs) into aquatic environments. Analytical techniques for NAs are challenged by sample complexity and interference from naturally occurring dissolved organic matter (DOM). Herein, we report the use of a poly­(dimethylsiloxane) (PDMS) polymer membrane for the on-line separation of NAs from DOM and use direct infusion electrospray ionization mass spectrometry to yield meaningful qualitative and quantitative information with minimal sample cleanup. We compare the composition of membrane-permeable species from natural waters fortified with a commercial NA mixture to those derived from weak anion exchange solid-phase extraction (SPE) using high-resolution mass spectrometry. The results show that SPE retains a wide range of carboxylic acids, including biogenic DOM, while permeation through PDMS was selective for petrogenic classically defined NAs (C n H2n+z O2). A series of model compounds (log K ow ∼1–7) were used to characterize the perm-selectivity and reveal the separation is based on hydrophobicity. This convenient sample cleanup method is selective for the O2 class of NAs and can be used prior to conventional analysis or as an on-line analytical strategy when coupled directly to mass spectrometry.

Aqueous-phase photochemical oxidation of water-soluble brown carbon aerosols arising from solid biomass fuel burning

“…and multifunctional internal standards (e.g., gemfibrozil) in complex sample matrices (e.g., waste water) and found bias to be within ± 15%. Additionally, several studies [60][61][62] have used single-functional compounds as an internal standard to identify a range of compounds in complex sample matrices during direct flow-injection MS analysis.…”

Photochemical formation of water-soluble oxyPAHs, naphthenic acids, and other hydrocarbon oxidation products from Cook Inlet, Alaska crude oil and diesel in simulated seawater spills

“…33 This process of photoproduction of NAs in HOPs from CI crude oil and diesel has, to the best of our knowledge, not been reported previously, and the doseresponse relationship of NAs merits further consideration. 30,[112][113][114][115][116][117]…”

Monitoring microplastic–contaminant sorption processes in real-time using membrane introduction mass spectrometry

“…PDMS is permeable to hydrophobic analytes and impermeable to water, particulate matter, ions, and hydrophilic compounds. 29 This allows for the direct observation of the free aqueous solution phase concentration of contaminants in complex heterogeneous solutions. 29 The technique has been coupled to electrospray ionization (ESI) which is well suited to measuring trace concentrations of organic amines 30 and carboxylic acids.…”

“…29 This allows for the direct observation of the free aqueous solution phase concentration of contaminants in complex heterogeneous solutions. 29 The technique has been coupled to electrospray ionization (ESI) which is well suited to measuring trace concentrations of organic amines 30 and carboxylic acids. 31 CP-MIMS can also be coupled to liquid electron ionization (LEI) and liquid electron ionization/chemical ionization (LEI/CI) ion sources for analysis of non-polar compounds such as polycyclic aromatic hydrocarbons (PAHs).…”