Selection criteria, solvents

A key criterion for selection of a solvent for electrochemical studies is the electrochemical stability of the solvent [12]. This is most clearly manifested by the range of voltages over which the solvent is electrochemically inert. This useful electrochemical potential window depends on the oxidative and reductive stability of the solvent. In the case of ionic liquids, the potential window depends primarily on the resistance of the cation to reduction and the resistance of the anion to oxidation. (A notable exception to this is in the acidic chloroaluminate ionic liquids, where the reduction of the heptachloroaluminate species [Al2Cl7] is the limiting cathodic process). In addition, the presence of impurities can play an important role in limiting the potential windows of ionic liquids. 

As with programmed temperature GC, the application of the Simplex optimization procedure to programmed solvent LC is relatively straightforward. The same procedure can be used both for isocratic and for gradient optimization, as long as an appropriate criterion is selected for each case. ... 

Selecting the proper solvent by considering this criterion is still based on empirical approaches because of the large nonideality of the resulting mixtures. However, general selection patterns and rapid experimental techniques have been made available through the years. This paper presents a review of some of these methods to facilitate the solvent selection process in the chemical industry. Qualitative aspects are first considered, followed by empirical correlations and rapid experimental techniques. 

The most important criterion for solvent selection is throughput, which mainly depends on a sufficient solubility of the solutes and the corresponding selectivity of the separation. Because solubility and selectivity depend on the interaction between the three elements of the chromatographic system, the selection of the mobile phase dependent on these parameters is further discussed in Section 4.3. 

As discnssed immediately above, an important criterion for solvent selection is solubility. The solvent mnst accommodate a reasonable amonnt of the species to be removed from the gas while still maintaining selectivity between the solnte(s) and carrier gas. When the carrier is air or an inert gas, it is easy to designate solnte vs. carrier in other cases, it is a matter of relative solnbility. Other criteria for solvent selection inclnde the following ... 

Sergeeva, K. Martinek, Denaturation capacity - a new quantitative criterion for selection of organic-solvents as reaction media in biocatalysis, Eur.J. Biochem. 1991,... 

As well as the solubility, the solvent release during and after application is another important criterion for solvent selection. Evaporation of the solvent mixture from the film is important not only for a smooth surface, but also for obtaining optimal, reproducible mechanical properties of the film. The boiling points or vapor pressures of the solvents do not provide sufficient information for formulating a paint system [3.12]. A model for calculating solvent evaporation also includes transport data of the solvents in the film in the form of diffusion parameters [3.13]. Evaporation behavior is also determined experimentally (e.g., according to ASTM D 3539.76). 

Nevertheless, the use of the UV cutoff value as the onty criterion for solvent selection leads to potentially missed opportunities for unique and powerful separations, as will be discussed in the following sections. 

Khmelnitsky, Y. L., V. V. Mozhaev, A. B. Belova, M. V. Sergeeva, and K. Martinek. 1991. Denaturation Capacity A New Quantitative Criterion for Selection of Organic Solvents as Reaction Media in Biocatalysis. European Journal of Biochemistry 198 (1) 31-41. 

To achieve a high value of Ki between the two phases. Si should tend to Si, i.e. the solute i should be similar to the stationary phase j = 1. Further, Kii should be different from K21 for any chromatographic separation between two solutes 1 and 2. Note that the two liquid phases must also be immiscible, for which, generally, (<5i -S2) >4 (Kar-ger et ah, 1973). There are many combinations of highly polar organic liquids and water where (i5i -1%) > 4 does not guarantee phase immiscibility. However, the criterion of liquid immiscibility is important for solvent selection. 

If the adhesive application method requires a solvent, the solubility parameter of the substrate is a significant criterion for solvent selection. In practical cases it is not uncommon to change the solvent blend to get a better bite into the surface. In more precise terms, the solubility parameter of the adhesive solution is being adjusted to achieve a higher degree of interaction between the adhesive and the substrate. 

The present chapter does not pretend to be an exhaustive record of Solid-Liquid calorimetry applications in Surface Science and Technology. It should be rather regarded as an introductory course with some illustrative examples. It is important to realise that the individual author s experience in the field has been the principal criterion for selection of specific instruments and their uses, without any intention of neglecting other contributions. The presentation of calorimetry methods will be restricted only to interfacial systems composed of a pure liquid or a dilute binary, at the most, solution in contact with a solid which does not dissolve in the liquid phase. This formalism may be still employed in the case of solutions which are not strictly binary but may be viewed as such (e.g., solutions containing ionizable solutes, background electrolytes or other additives that may be lumped together as constituting a mean solvent or a mean solute). 

The solvent plays an important role in determining the ultimate membrane properties and performance. The most important criterion for solvent selection is its ability to dissolve the polymer fully. The commonly used organic solvents to prepare PVDF membranes through immersion precipitation are dimethyl formamide (DMF) (Gugliuzza and Drioli 2009), DMA (Lin et al. 2003 Yeow et al. 2005 Yan et al. 2006),... 

Another aspect of cost reduction would be solvent economy. The need to preferentially select inexpensive solvents and employ the minimum amount of solvent per analysis would be the third performance criteria. Finally, to conserve sample and to have the capability of determining trace contaminants, the fourth criterion would be that the combination of column and detector should provide the maximum possible mass sensitivity and, thus, the minimum amount of sample. The performance criteria are summarized in Table 1. Certain operating limits are inherent in any analytical instrument and these limits will vary with the purpose for which the instrument was designed. For example, the preparative chromatograph will have very different operating characteristics from those of the analytical chromatograph. 

Nevertheless, in some cases, this criterion is not sufficient for the choice of the solvent. For instance, Kuo and Parkin [78], demonstrated that hydrophobicity of solvent in the presence of lipase also affect selectivity and partition of reactants in esterification reactions. On the other hand, in the presence of certain solvents, even in low concentration, enzyme can be activated [13]. 

This sub-problem considers the mixture properties. Mixture properties can be categorized into two types. Properties such as selectivity, solvent power etc., are based on infinite dilution activity coefficients, which are independent of composition and hence only structural information is needed for their calculation. Properties such as complete or partial miscibility of solvent with another constituent is handled by discritizing the composition range from 0 to 1 into n divisions and verifying the miscibility criterion at those points. The difference between pure component property constraints and mixture property constraints is that the former are linear and the latter are non-linear. Those satisfying the mixture property constraints are further analyzed in sub-problem 4. 

Particle class Protein Separation vs Concentration Separation Optimization criterion Purity Assoc/Dissoc in sucrose No Sedimentation coefficient 16.0 10-40% or 5-20% gradient 10-40 Sample form liquid/semi-solid Total sample volume (mL) 3.0 Sample concentration % w/w 1.0 Selected final location 45.0 Solvents No... 

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