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.
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