posted on 2020-03-09, 12:34authored byJuliana R. Laszakovits, Arpad Somogyi, Allison A. MacKay
Dissolved
organic matter (DOM) is ubiquitous in raw drinking water
and can efficiently scavenge oxidants, such as permanganate. Here,
changes to DOM induced by permanganate oxidation under typical drinking
water treatment conditions (6 μM, 1 h) to bulk DOM properties,
DOM functional groups, and DOM chemical formulae were examined for
two DOM isolate types (terrestrial and microbial). Permanganate oxidation
did not mineralize DOM, rather changes were compositional in nature.
Optical properties suggest that permanganate oxidation decreased DOM
aromaticity (decreased SUVA-254), decreased DOM electron-donating
capacity, and decreased DOM average molecular weight (increased E2/E3
ratios). Fourier-transform-infrared spectroscopy second derivative
analyses revealed that permanganate does not oxidize DOM alkene groups,
suggesting permanganate access to functional groups may be important.
Four ionization techniques were used with ultrahigh-resolution mass
spectrometry: negative and positive ion mode electrospray ionization
and negative and positive ion mode laser/desorption ionization. The
results from all four techniques were combined to understand changes
in DOM chemical formulae. It was concluded that nitrogen-containing
aromatic compounds and alkylbenzenes were oxidized by permanganate
to form nitrogen-containing aliphatic compounds and benzoic acid-containing
compounds. This work highlights how multiple ionization techniques
coupled with UHR-MS can enable a more detailed characterization of
DOM.