Partition anionic species

The thermodynamics of the extraction mechanism is extremely complex. In the initial equilibration of the ion pairs (Scheme 1.6) account has to be taken not only of the relative stabilities of the ion-pairs but also of the relative hydration of the anionic species. Assuming the complete non-solvation of the ion-pairs, the formation of the ion-pair [Q+Y] will generally be favoured when the relative hydration of X- is greater than that of Y. However, in many cases, the anion of the ion-pair is hydrated [8-11] (Table 1.1) and this has a significant effect both on equilibrium between the ion-pairs in the aqueous phase and the relative values of the partition coefficients of the two ion-pairs [Q+X ] and [Q+Y ] between the two phases. 

The partition coefficients for the anionic species were at least two orders of magnitude higher in the liposome system than in octanol. 

The importance of lipids in bioconcentration is emphasized several times in this chapter, and various devices have been explored to take this into account. Experiments using liposomes prepared with L-a-dipalmitoyl and L-a-dio-leylphosphatidylcholine, and membranes prepared from Rhodobacter sphaeroides were therefore studied in an attempt to produce more realistic models of the lipid phase in partition experiments (Escher and Schwartzen-bach 1996). The system was evaluated using a number of phenols of varying pKa and log Kow values, and it was shown that both systems provided good models for all species of phenolic compounds. An extremely important observation that has wide implications for ecotoxicology emerged not only the neutral phenols partitioned into the liposomes but also the anionic species. 

For metal desorption from the biomass certain dilute solutions of mineral acids like hydrochloric acid, sulfuric acid, acetic acid and nitric acid were used [219, 76]. Batch system was carried out to study the desorption of the adsorbed Hg (II) from the biosorbent - immobilized and heat inactivated Trametes versicolor and Pleurotus sajur-caju [8]. Hg (II) ions adsorbed onto the biosorbents were eluted with 10 mmol dm HCl and the results showed that more than 97% of the adsorbed Hg (II) ions were desorbed from the biosorbents. In order to evaluate the feasibility of applying the prepared biosorbents in the heavy metals removal processes, the metal desorption efficiency from loaded biosorbents, and the reusability of the biosorbent in repeated adsorption-desorption operations were determined. The charged species exhibited desorption-resistance fraction whereas the desorption of the neutral form was completely reversible. The difference in sorption and desorption between the neutral and charged species is attributed to the fact that the anionic species sorbs by a more specific exothermic adsorption reaction whereas the neutral form partition by the hydrophobic binding to the soil [206]. Desorption of soil-associated metal ions and possible mechanisms have received considerable attention in literature [148],... 

To distinguish partition coefficients of neutral species from ionized species, the notation log PN and log/j/ may be used, respectively, or the symbol C or A may be used as a substitute for superscript /, denoting a cation or anion, respectively. [362],... 

---