Feasible concentrations from potentials

Introducing the chemical potential (or free energy) and the thermodynamic constraint provides a solid physical chemistry foundation for the constraint-based analysis approach to metabolic systems analysis. Treatment of the network thermodynamics not only improves the accuracy of the predictions on the steady state fluxes, but can also be used to make predictions on the steady state concentrations of metabolites. To see this, we substitute the relation between reaction Gibbs free energy (ArG ) of the th reaction and the concentrations of biochemical reactants 

Here (A rG °)j is the standard transformed equilibrium Gibbs free energy for reaction j, which may be obtained from a standard chemical reference source. 

If a flux vector J is thermodynamically feasible, then there exist concentrations Ci that satisfy the above inequality. In fact, Equation (9.27) defines a feasible space for the metabolites concentrations as a convex cone in the log-concentration space. 

If the set of feasible concentrations is empty, then the vector J =. /, is thermodynamically infeasible. 

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In batch processing aggressive reactants are, typically, diluted to prevent thermal overshooting and runaway. Even then they often are added drop-wise, to allow heat transfer to be adjusted to heat release. In some cases, this may take over half an hour or so. This unnecessarily prolongs processing time and, also, the reaction then is carried out for a considerable part under totally changing reactant concentrations (from zero to full-load content). Conversely, microreactors with their efficient heat and mass transfer have the potential to contact the full reactant load all at once . In addition, microreactors can cope with concentrated solutions or even piue liquid reactants. Several examples are known for which such all at once or solvent-free procediues are feasible in microreactors with reasonable selectivity, whereas the... 

The contaminants of concern can be isolated and concentrated into a reduced volume which can be more easily handled. Another potential benefit of the concentration process is that additional destructive treatment alternatives may become feasible. For example, the concentration of hydrocarbons from a contaminated groundwater can produce a reduced volume waste with a high BTU value allowing for fuel blending as a disposal alternative. This not only reduces the quantity of groundwater that must be treated, but also produces a more easily treatable final waste product. As another example, heavy metals can be concentrated from an aqueous stream by membrane processes and immobilized by solidification/stabilization technologies. 

Thus, co-deposition of silver and copper can take place only when the silver concentration in the electrolyte falls to a very low level. This clearly indicates that the electrolytic process can, instead, be used for separating copper from silver. When both silver and copper ions are present, the initial deposition will mainly be of silver and the deposition of copper will take place only when the concentration of silver becomes very low. Another example worth considering here is the co-deposition of copper and zinc. Under normal conditions, the co-deposition of copper and zinc from an electrolyte containing copper and zinc sulfates is not feasible because of the large difference in the electrode potentials. If, however, an excess of alkali cyanides is added to the solution, both the metals form complex cyanides the cuprocyanide complex is much more stable than the zinc cyanide complex and thus the concentration of the free copper ions available for deposition is considerably reduced. As a result of this, the deposition potentials for copper and zinc become very close and their co-deposition can take place to form alloys. 

The truncated peptide analogs were used to demonstrate the specificity of the method and to evaluate the limit of quantitation of potential impurities. Potential impurities were spiked into a solution of IB-367 at 0.05%, 0.1%, 0.2%, 0.5%, and 1% to assay the linearity of potential impurities at low concentrations. The method exhibited acceptable linearity for impurities from 0.05 to 1%. The relative response factors of these analogs were assessed to determine area normalization feasibility. 

The isolation method of solvent extraction has been suggested as a potentially feasible process to concentrate trace organic compounds from finished drinking water (4). One positive attribute of the solvent extraction method is that its performance for any given compound is theoretically predictable from a partition coefficient of a compound between the water sample and an organic solvent. The partition coefficient can be experimentally determined for any solute in any two-phase solvent system (7, 8). Variables of the extraction procedure such as solvent-to-water ratio and the choice of solvents can be adjusted to achieve optimum recovery. 

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