Modelling Chemical Speciation: Thermodynamics, Kinetics and Uncertainty

Chemical speciation refers to the distribution of an element amongst chemical species in a system. It is critical for understanding chemical toxicity, bioavailability, and environmental fate and transport. Despite the central importance of knowing the full speciation of a chemical in order to predict its behaviour in a system, it is generally not possible to determine a speciation analysis using analytical chemistry methods alone. Most techniques are focused on detection of free metal ion concentrations (e.g., Galceran et al., 2004; Salaun et al., 2003; Zeng et al., 2003) or total metal concentrations (e.g., Wang et al., 1998). Direct speciation measurement using traditional analytical methods requires significant complexity and generally hyphenated techniques (Sanzmedel, 1995; Yan and Ni, 2001; Moldovan et al., 2004). A relatively new method, capillary electrophoresis (CE), allows direct measure of chemical speciation of some metals (Haumann and Bachmann, 1995; Beale, 1998; Dabek-Zlotorzynska et al., 1998). However, because environmental concentrations of most metals of interest are low, and because many relevant forms of metals cannot be measured directly, analytical techniques often are not effective for determining overall speciation (Fytianos, 2001). Thus chemical speciation determination generally relies on utilising analytical methods in conjunction with chemical speciation models.