Species sensitivity distributions United States

The pH of the solution is also an important parameter that will influence the luminescence characteristics of organic species that exhibit acid-base properties. In many instances, the chemical and physical properties of electronically excited molecules differ markedly from those of the ground-state molecules, because of the different electronic distribution. Therefore, most of the excited molecules show protonation constants (log Kg) which differ greatly from those measured in their ground states. Differences in log Kg of more than 6 units have been observed in a variety of compounds. As for the ground state, acid-base equilibria in the excited state are drastically altered by the surfactant aggregates, which can result in a further increase in sensitivity. 

Transport of a species through a liquid membrane is superior to solvent extraction (SX) since extraction and stripping are performed in a single unit operation. Also, liquid membrane transport is a non-equilibrium, steady state process which depends upon kinetic factors in contrast to SX which is an equilibrium process. Furthermore, even solvents with low distribution coefficients for Ae desired species may be utilized in LM processes. Although LM systems generally have slower rates than ion-exchange (DC) processes, the latter are particularly sensitive to the presence of suspended solids and other foulants and also must be operated in cycles. 

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