Direct, Isomer-Specific Quantitation of Polycyclic Aromatic Hydrocarbons in Soils Using Membrane Introduction Mass Spectrometry and Chemical Ionization

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are routinely screened for in soils, where quantitation of structural isomers is critical due to varying toxicity within PAH isomer classes. While chromatographic methods provide isomer resolution, such strategies are cost and time intensive. To address these challenges, we present condensed phase membrane introduction mass spectrometry using liquid electron ionization/chemical ionization (CP-MIMS-LEI/CI) as a direct mass spectrometry technique that provides rapid, quantitative results for PAH isomer measurements in soil samples. A methanol acceptor phase is flowed through a probe-mounted polydimethylsiloxane hollow fiber membrane directly immersed into a dichloromethane/soil slurry. PAHs and dichloromethane co-permeate the membrane into the acceptor solvent, whereas particulates and charged matrix components remain in the sample. A nanoflow of the membrane permeate is then directly infused into a LEI/CI interfaced triple quadrupole mass spectrometer. Diagnostic PAH adduct ions were formed at either M + 45 ([M + CH2Cl + CH3OH–HCl]+) or M + 47 ([M + CHCl2–HCl]+). This allowed the development of specific MS/MS transitions for individual PAH isomers. These transitions were subsequently used for the direct analyses of PAHs in real soils where CP-MIMS-LEI/CI was shown to be rapid (15 soil samples/h) and sensitive (ng/g level detection limits). CP-MIMS-LEI/CI results compared well to those obtained using GC–MS (average percent difference of −9% across 9 PAHs in 8 soil samples), presenting a compelling argument for direct, quantitative screening of PAHs in soils by CP-MIMS-LEI/CI, particularly given the simple workflow and short analytical duty cycle.

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

“…It should be noted that many of the constituents in the broader class of NA fraction compounds, which include heteroatoms (N, S) and additional O, are sufficiently polar or remain ionized in solution and therefore not sampled by membrane extraction. While other hydrophobic compounds, such as polycyclic aromatic hydrocarbons, are known to permeate the PDMS membrane, they do not bias the results presented here, as they are not ionized by ESI(−). On the other hand, some nonpetrogenic carboxylic acids (i.e., resin acids from the pulp and paper industry) may impart a positive bias, if present.…”

A Direct Mass Spectrometry Method for the Rapid Analysis of Ubiquitous Tire-Derived Toxin N-(1,3-Dimethylbutyl)-N′-phenyl-p-phenylenediamine Quinone (6-PPDQ)

“…CP-MIMS typically employs a semipermeable polydimethylsiloxane (PDMS) capillary hollow fiber membrane (CHFM) to separate hydrophobic analytes from interfering matrix components (e.g., salts and particulate matter) directly in liquid/slurry samples. , An organic acceptor continuously passed through the CHFM transports permeating analytes to the MS ion source. , This approach has been paired with both electrospray ionization (ESI) − and liquid electron ionization (LEI), − enabling direct measurements of a wide array of analytes in diverse, complicated matrices, including PAHs in natural waters and sediments, , naphthenic acids in constructed wetlands and oil-affected waters, pharmaceuticals in wastewater, and fatty acids in fish . The perm-selectivity of analytes with acid/base properties is pH-dependent and has been used to derive the p K a of trace organics in water .…”

Liquid Chromatography–Electron Capture Negative Ionization–Tandem Mass Spectrometry Detection of Pesticides in a Commercial Formulation

“…Vandergrift et al exploited the LEI interface coupled with condensed phased membrane introduction mass spectrometry (CP-MIMS) with a conventional CI source, demonstrating that the acceptor phase solvent can provide suitable reagent species in the positive ion mode (PCI) for the analysis of dialkyl phthalates and polycyclic aromatic hydrocarbons in dust and soils, respectively. , …”