Abstract : Sorptive fractionation of Suwannee River Fulvic Acid (SRFA) and Purified Aldrich Humic Acid (PAHA) on $\alpha$-Al$_2$O$_3$ at pH 6 was probed in the supernatant using different spectroscopic techniques. Comparison of dissolved organic carbon (DOC) analysis with UV/Vis spectrophotometric measurements at 254 nm, including Specific UV absorbance (SUVA) calculation, revealed a decrease in chromophoric compounds for the non sorbed extracts after a 24 h contact time. This fractionation, only observable below a certain ratio between initial number of sites of humic substances and of $\alpha$-Al$_2$O$_3$, seems to indicate a higher fractionation for PAHA. C(1s) near-edge X-ray absorption fine structure spectroscopy (NEXAFS) confirmed this trend and points to a decrease in phenolic moieties in the supernatant and to an eventual increase in phenolic moieties on the surface. Time-resolved luminescence spectroscopy (TRLS) of Eu(III) as luminescent probe showed a decrease in the ratio between the $^5$D0$\rightarrow$$^7$F$_2$ and $^5$D0$\rightarrow$$^7$F$_1$ transitions for the fractionated organic matter (OM) that is thought to be associated to a lower energy transfer from the OM to Eu(III) due to the loss of polar aromatics. These modifications in the supernatant are a hint for the modification of sorbed humic extracts on the surface.
Francis Claret, Thorsten Schäfer, Julien Brevet, Pascal E. Reiller. Fractionation of Suwannee River fulvic acid and Aldrich humic acid on $\alpha$-Al$_2$O$_3$: spectroscopic evidence. Environmental Science and Technology, American Chemical Society, 2008, 42 (23), pp.8809-8815. ⟨10.1021/es801257g⟩. ⟨cea-00344262⟩