soil, and complexation with metal oxides contributes significantly to the overall
sorption capacity. These studies have systematically investigated the influence of
competing inorganic cations that are naturally available in soils as well as the
influence of pH, different types of minerals, and the structure of the considered
cations (Droge and Goss 2012a, b, 2013b; Jolin et al. 2017; MacKay and Seremet
2008; MacKay and Vasudevan 2012; Pils and Laird 2007; Sassman and Lee 2005;
Tolls 2001). It was found that the ionic species contributes significantly to the total
sorption of ionizable organic bases, even if the fraction of the ionic species is not
dominating (Droge and Goss 2012b). For anionic organic species, sorption in soils
is less pronounced due to the rather small anion exchange capacity, but still not
negligible (Higgins and Luthy 2006; Rodriguez-Cruz et al. 2005; Tülp et al. 2009).
For zwitterions it was shown that both charged functions of the molecule can matter
so that the sorption process becomes even more complex (Carrasquillo et al. 2008;
Figueroa and MacKay 2005; MacKay and Seremet 2008).
The sorption of IOCs to different types of polymers has also been studied.
Finding a polymer that has a reasonably high sorption capacity for charged
chemicals is challenging, but it is the prerequisite for successful solid phase
microextraction (SPME) and passive sampling of IOCs (Bäuerlein et al. 2011).
Polyacrylate (PA) has been used for SPME of weak organic acids and bases
(Broeders et al. 2011; Escher et al. 2002; Haftka et al. 2013; Ohlenbusch et al.
2000). However, only the neutral species of these chemicals partitions to PA and
permanently charged IOCs can only be sampled, if the molecule has a large
hydrophobic tail (e.g., surfactants) (Chen et al. 2012; Rico-Rico et al. 2009).
Recently, C18 based materials have been reported to be suitable sorption materials
for IOCs (Henneberger et al. 2019; Peltenburg et al. 2015b; Vuckovic et al. 2009).
Peltenburg et al. have successfully used the so-called mixed-mode SPME fibers that
combine hydrophobic C18 and cation exchange groups for sampling of organic
bases (Peltenburg et al. 2013, 2015a, b, 2016). Ion exchange polymers were also
used as sorption materials for IOCs (Bäuerlein et al. 2011). In fact, ions of opposite
charge show high affinities for ion exchange polymers, but the material has to be
thoroughly calibrated, because sorption is nonlinear (i.e., concentration dependent)
and highly influenced by the concentration of other ions present in the solution
(Bäuerlein et al. 2012; Oemisch et al. 2014).
5 Modeling of Ion Sorption
In contrast to neutral chemicals, the modeling of organic ions´ sorption is still limited
to several specific modeling approaches mostly with small domains of applicability.
For neutral chemicals the octanol–water partition constant (K ow ) is often used to
model sorption to biological phases. This approach has been extended to ionizable
chemicals as well. The simplest sorption model for ionizable chemicals is shown in
Eq. 1. In this equation, the pH-dependent distribution ratio between octanol and
water (D ow (pH)) for an ionizable chemical is calculated from the octanol–water
Environmental Sorption Behavior of Ionic and Ionizable Organic Chemicals
51
sorption capacity. These studies have systematically investigated the influence of
competing inorganic cations that are naturally available in soils as well as the
influence of pH, different types of minerals, and the structure of the considered
cations (Droge and Goss 2012a, b, 2013b; Jolin et al. 2017; MacKay and Seremet
2008; MacKay and Vasudevan 2012; Pils and Laird 2007; Sassman and Lee 2005;
Tolls 2001). It was found that the ionic species contributes significantly to the total
sorption of ionizable organic bases, even if the fraction of the ionic species is not
dominating (Droge and Goss 2012b). For anionic organic species, sorption in soils
is less pronounced due to the rather small anion exchange capacity, but still not
negligible (Higgins and Luthy 2006; Rodriguez-Cruz et al. 2005; Tülp et al. 2009).
For zwitterions it was shown that both charged functions of the molecule can matter
so that the sorption process becomes even more complex (Carrasquillo et al. 2008;
Figueroa and MacKay 2005; MacKay and Seremet 2008).
The sorption of IOCs to different types of polymers has also been studied.
Finding a polymer that has a reasonably high sorption capacity for charged
chemicals is challenging, but it is the prerequisite for successful solid phase
microextraction (SPME) and passive sampling of IOCs (Bäuerlein et al. 2011).
Polyacrylate (PA) has been used for SPME of weak organic acids and bases
(Broeders et al. 2011; Escher et al. 2002; Haftka et al. 2013; Ohlenbusch et al.
2000). However, only the neutral species of these chemicals partitions to PA and
permanently charged IOCs can only be sampled, if the molecule has a large
hydrophobic tail (e.g., surfactants) (Chen et al. 2012; Rico-Rico et al. 2009).
Recently, C18 based materials have been reported to be suitable sorption materials
for IOCs (Henneberger et al. 2019; Peltenburg et al. 2015b; Vuckovic et al. 2009).
Peltenburg et al. have successfully used the so-called mixed-mode SPME fibers that
combine hydrophobic C18 and cation exchange groups for sampling of organic
bases (Peltenburg et al. 2013, 2015a, b, 2016). Ion exchange polymers were also
used as sorption materials for IOCs (Bäuerlein et al. 2011). In fact, ions of opposite
charge show high affinities for ion exchange polymers, but the material has to be
thoroughly calibrated, because sorption is nonlinear (i.e., concentration dependent)
and highly influenced by the concentration of other ions present in the solution
(Bäuerlein et al. 2012; Oemisch et al. 2014).
5 Modeling of Ion Sorption
In contrast to neutral chemicals, the modeling of organic ions´ sorption is still limited
to several specific modeling approaches mostly with small domains of applicability.
For neutral chemicals the octanol–water partition constant (K ow ) is often used to
model sorption to biological phases. This approach has been extended to ionizable
chemicals as well. The simplest sorption model for ionizable chemicals is shown in
Eq. 1. In this equation, the pH-dependent distribution ratio between octanol and
water (D ow (pH)) for an ionizable chemical is calculated from the octanol–water
Environmental Sorption Behavior of Ionic and Ionizable Organic Chemicals
51