Evaluation of amphiphilic properties of fulvic acid and humic acid by alkylpyridinium binding study

Predictive model of cationic surfactant binding to humic substances

“…Koopal et al [29] have shown the influence of pH and cationic surfactant aliphatic chain length on the binding of cationic surfactants to HA. In a similar study Yee et al [21] have measured cationic surfactant binding to HA and FA and the results were analyzed using the Hill and the Langmuir equation. The surfactant binding to FA could be described with the Hill equation; it showed, close to the critical micelle concentration of the surfactants, a strong cooperativity that was not present with the binding to HA.…”

“…Direct studies of surfactant binding to HS are limited and more recent [21,22,29,30]. Koopal et al [29] have shown the influence of pH and cationic surfactant aliphatic chain length on the binding of cationic surfactants to HA.…”

“…Recently also protein binding to HS has been studied [15,16] and some studies exist on the role that HS have on enzyme activities [17]. HS also can bind low molar mass organic pollutants [18][19][20][21][22], but here the knowledge of the effect of environmental conditions such as pH and salt concentration on the binding is mainly limited to surfactant binding.…”

“…[30] investigated the effects of chain length, salt ion concentration and the presence of heavy metal cations on the binding of cationic surfactants to HA. Although some modeling attempts have been made [21], unraveling of the electrostatic and specific interactions that contribute to the surfactant binding to HS, as done for ion binding, has not yet been considered. Only by considering both types of interactions explicitly models based on intrinsic binding parameters can be obtained that allow the prediction of the surfactant binding to HA and FA as a function of surfactant concentration, pH and salt concentration.…”

Humic substance charge determination by titration with a flexible cationic polyelectrolyte

“…The charge density of HS depends on the pH and at the pH conditions in most natural waters HS are negatively charged (Milne et al, 1995;Ritchie and Perdue, 2003). The charge density of humic particles is a dominant factor for the interactions of HS with: (1) heavy metal ions (Milne et al, 2003;Koopal et al, 2005;Merdy et al, 2006), (2) oppositely charged polyelectrolytes (Bolto et al, 1999;Kam and Gregory, 2001;Hankins et al, 2006), (3) proteins (Tan et al, 2008(Tan et al, , 2009), (4) cationic surfactants Yee et al, 2006;Ishiguro et al, 2007) and (5) mineral surfaces Filius et al, 2000;Saito et al, 2004;Weng et al, 2005). Therefore, for a good understanding of these interactions reliable information on charge characteristics of HS is of vital importance.…”