Using Spectrophotometric Titrations To Characterize Humic Acid Reactivity at Environmental Concentrations

Abstract

Potentiometric titration is a common method to characterize dissolved organic matter (DOM) reactivity. Because of the sensitivity of pH electrodes, it is necessary to work with very high DOM (>1 g/L) concentrations that are unrealistic compared to those found in natural waters (0.1 to 100 mg/L). To obtain proton binding data for concentrations closer to environmental values, spectroscopic titration methodology is a viable alternative to traditional potentiometric titrations. Spectrophotometric titrations and UV-visible spectra of a diluted solution of purified Aldrich humic acid (5 mgDOC/L) are used to estimate changes in proton binding moieties as function of pH and ionic strength after calculation of differential absorbance spectra variations. After electrostatic correction of spectrophotometric data, there is a linear operational correlation between spectrophotometric and potentiometric data which can be used as a transfer function between the two properties. Spectrophotometric titrations are then used to determine the changes of humic acid protonation after adsorption onto alpha-alumina.

Depth-dependent molecular composition and photo-reactivity of dissolved organic matter in a boreal lake under winter and summer conditions

“…This was important to avoid changes in the pH-dependent shift in absorbance and photobleaching as described elsewhere (Pace et al, 2012;Janot et al, 2010). The samples were then divided and half of the sample (20 mL) was continuously pumped through a custom-built photo reactor cell made out of Tefzel tubing for 24 h. A 10 mL gas equilibrator was also attached in-line to allow saturation of air gases at any given time.…”

Europium(III) complexed by HPSEC size-fractions of a vertisol humic acid: Small differences evidenced by time-resolved luminescence spectroscopy

“…5. This model may appear too simplistic, but (i) the amount of the different fractions was not sufficient to perform reliable acid-base titrations [30], and (ii) the application of generic parameters, as those selected otherwise [28,29,61], may not be directly applied to our case. As by our approach, the magnitude of logˇ(complexation strength) was not the most influencing parameter, while it was instead the number of available complexation sites that explained most of modifications in GHA separated fractions.…”

“…Christl et al showed that the functionality [28] and metal binding [29] of different size-fractions of a HA from ultrafiltration were comparable within a narrow range. Conversely, Hur and Schlautman [25], Reiller et al [27] and Janot et al [30] showed that clear modification occurred on mass-distribution and acid-base properties of HA after sorptive fractionation. In addition, Claret et al [26] noted that the influence of sorptive fractionation of HS on ␣-Al 2 O 3 was important from the evolution of the chemical environment of europium(III) by time-resolved luminescence spectroscopy (TRLS).…”

Effects of calcium on the chromophores of dissolved organic matter and their interactions with copper

“…The absorbance of DOM is also sensitive to DOM interactions with the proton and metal cations (Dryer et al, 2008;Janot et al, 2010;Yan et al, 2013a;Yan and Korshin, 2014). In absorbance measurements, the concept of differential absorbance allows ascertaining the general types of the involved functional groups and extent of their interactions with protons and metal cations.…”