Structure-dependent reactivity of low molecular weight fulvic acid molecules during ozonation.
Size-exclusion chromatography coupled to quadrupole time-of-flight mass spectrometry (SEC-Q-TOF-MS) was used to study changes in the molecular composition of a Suwannee River fulvic acid isolate by ozonation. The composition of all three SEC fractions showed strong changes and a relative increase of the low molecular weight anions. Further mass spectrometric investigations focused on the low molecular weight fulvic acid molecules, where a preferential removal of fulvic acid molecules with a low oxidation state (low O/C ratio) and a high degree of unsaturation (low H/C ratio) was observed. Besides their elemental composition, also the structure of the fulvic acid molecules influenced their reactivity toward ozone. The data suggestthat molecules with a more extended carbon skeleton and less carboxylate substituents showed higher reactivitywhereas some highly unsaturated molecules did not show measurable removal up to a specific ozone dose of 2.5 mg/mg of DOC due to sterical shielding of the reactive structures. Newly formed molecules were determined by SEC-Q-TOF-MS, which were characterized by a very high number of carboxylate groups (high O/C ratio) and a highly saturated carbon skeleton (high H/C ratio). These investigations explain on a molecular level many observations previously made with whole mixtures or fractions of natural organic matter.
These
Anja
A
Department of Water Quality Control, Technical University of Berlin, Sekr KF 4, Strasse des 17 Juni 135, 10623 Berlin, Germany.
Reemtsma
Thorsten
T
D001578:Benzopyrans / Q000737:chemistry*; D002850:Chromatography, Gel; D013058:Mass Spectrometry; D015394:Molecular Structure; D008970:Molecular Weight; D010126:Ozone / Q000737:chemistry*
D001578:Benzopyrans; D010126:Ozone; C005023:fulvic acid