Selectivity of separation

In the course of mixture separation, the composition and properties of both mobile phase (MP) and stationary phase (SP) are purposefully altered by means of introduction of some active components into the MP, which are absorbed by it and then sorbed by the SP (e.g. on a silica gel layer). This procedure enables a new principle of control over chromatographic process to be implemented, which enhances the selectivity of separation. As a possible way of controlling the chromatographic system s properties in TLC, the pH of the mobile phase and sorbent surface may be changed by means of partial air replacement by ammonia (a basic gaseous component) or carbon dioxide (an acidic one). 

Catechin and epicatechin are two flavanols of the catechin family. They are enantiomers. The capillary zone electrophoresis (CE) methods with UV-detection were developed for quantitative determination of this flavanols in green tea extracts. For this purpose following conditions were varied mnning buffers, pH and concentration of chiral additive (P-cyclodextrin was chosen as a chiral selector). Borate buffers improve selectivity of separation because borate can make complexes with ortho-dihydroxy groups on the flavanoid nucleus. 

Definition of process objectives Generation of separation core structure Selection of separation sequence and unit operations Addition of further units to the process structure Selection of crystallizer type... 

Most size exclusion chromatography (SEC) practitioners select their columns primarily to cover the molar mass area of interest and to ensure compatibility with the mobile phase(s) applied. A further parameter to judge is the column efficiency expressed, e.g., by the theoretical plate count or related values, which are measured by appropriate low molar mass probes. It follows the apparent linearity of the calibration dependence and the attainable selectivity of separation the latter parameter is in turn connected with the width of the molar mass range covered by the column and depends on both the pore size distribution and the pore volume of the packing material. Other important column parameters are the column production repeatability, availability, and price. Unfortunately, the interactive properties of SEC columns are often overlooked. 

Jandera, P., Correlation of retention and selectivity of separation in reversed-phase high-performance liquid chromatography with interaction indices and with lipophilic and polar structural indices, J. Chromatogr. A, 656, 437, 1993. 

The starting point in the development and designing of a closed water loop system is an inventory of the amounts and the quality of the process and transport water flows which are needed for the various steps in the production process. Each production step where process or transport water is involved causes a certain amount of wastewater. The pollution of this water is strongly dependent on the process step. The selection of separate treatment steps which, together, comprise a closed loop water system is complex. As already mentioned, various complete treatment scenarios can be developed and designed to satisfy the requirements set for process and transport water and treatment of wastewater. A technical and economic evaluation, in combination with environmental sustainability assessment, is necessary to determine the treatment system which is most appropriate. 

The selectivity of separation is mainly affected by parameters of the bulk electrolyte in the capillary. These include type of anion and cation, pH, ionic strength, concentration, addition of modifiers such as com-plexing agents, organic solvents, surfactants, etc. It is expressed in terms of mobility differences (A/i) or the mobility ratio s (a) ... 

This means that the effective mobility will depend on their pK in relation to the pH of the BGE. For weak bases, the analyte will be practically fully protonated (BH ) at pHpartially protonated at pipHpIweak acid which will be practically non-ionized at pHpartially ionized at p A—2pipi[Pg.327]

The performance and capacity advantages of alkaline batteries vs carbon—zinc is resulting in the continuous decline of this battery. The low cost of the carbon zinc cell is a major reason for its continued use. Thus, cost is a major consideration in the development and selection of separators for this system. 

However, the unexpectedly increased selectivity in the synergistic Am -Eu system with CYANEX 301 and some O-bearing weak-base coextractants [45] shows that still other factors, for example different participation of the lanthanide and actinide /-orbitals in bonding, must be taken into account when considering the selectivity of separation. 

By appropriate choice of the type (or combination) of the organic solvent(s), selective polar dipole-dipole, proton-donor, or proton-acceptor interactions can be either enhanced or suppressed and the selectivity of separation adjusted [42]. Over a limited concentration range of methanol-water and acetonitrile-water mobile phases useful for gradient elution, semiempirical retention equation (Equation 5.7), originally introduced in thin-layer chromatography by Soczewinski and Wachtmeister [43], is used most frequently as the basis for calculations of gradient-elution data [4-11,29,30] ... 

However, the most promising results are obtained when quebracho at pH 11 is used. A selectivity of separation over a wide particle size range is obtained (43). 

SELECTION OF SEPARATION PROCESS BY PARTICLE SIZE CONTAMINATION LEVEL... 

The first step in calculating fluid properties is selection of separator conditions. There may be circumstances for a particular field which dictate a specific separator pressure. If not, the separator pressure which produces the maximum amount of stock-tank liquid is selected. This pressure is known as optimum separator pressure. It is identified from the separator tests as the separator pressure which results in a minimum of total gas-oil ratio, a minimum in formation volume factor of oil (at bubble point), and a maximum in stock-tank oil gravity ( API). Most black oils have optimum separator pressures of 100 to 120 psig at normal temperatures. 

Selection of Separator Conditions—Formation Volume Factor of Oil—Solution Gas-Oil Ratio — Formation Volume Factor of Gas—Total Formation Volume Factor— Viscosities — Coefficient of Isothermal Compressibility of... 

The selectivity of separation does not change in the course of the voltage programming, making method development easy and straightforward. 

Every single regeneration problem has to be analysed individually, however, the following case study demonstrates how a selection of separation techniques, extraction and phase separation, can successfully be applied to regenerate a spent ionic liquid based electrolyte satisfactorily. As a case study the electrolyte 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)amide ([BMP]Tf2N) was chosen, which is used for electrodeposition of aluminum as described in the literature [137, 138],... 

Dual cyclodextrin systems can be developed to provide impressive selectivity of separation [30—32], A typical recipe uses 0.5-1 mM of a charged CD and 5-10 mM of a neutral CD. The development of a dual-CD system chiral separation of secondary amine drug substances is illustrated in Figure 4 using various blends of CDs. A complete separation is only found in run (d), where the buffer contained 5 mM of a neutral and 1 mM of a charged CD. 

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