Selectivity in programmed solvent

The selectivity in programmed solvent LC may be varied by varying the solvents used or by the application of ternary or even more complicated gradients. However, most ternary gradients can in fact be reduced to binary ones using mixed (pseudo-) solvents. 

The most useful secondary parameter for the optimization of the selectivity in programmed solvent LC is the nature of the modifter(s) in the mobile phase. The selectivity can be varied by selecting various solvents (pure solvents for binary or ternary gradients mixed solvents for pseudo-binary gradients). Analogous to the situation in isocratic LC, it is possible to use different modifiers (and hence to obtain different selectivity) while optimum retention conditions are maintained for all solutes. This possibility to optimize the selectivity in programmed solvent LC will be discussed below. 

The application of the Simplex procedure for the optimization of the selectivity in programmed solvent LC (e.g. for the application of ternary gradients) has not yet been reported. However, there is no apparent obstacle to the applicability of the Simplex procedure for this purpose. 

Three methods appear to be available for optimizing the selectivity in programmed solvent LC ... 

In programmed solvent LC the nature of the modifier(s) in the mobile phase is the most common secondary parameter that may be used for the optimization of the selectivity. This is an attractive parameter, because different modifiers may be selected and programmed automatically on various commercial instruments. Therefore, the possibilities for selectivi-... 

The (primary) program parameters may be used to optimize the separation in programmed solvent LC in a non-selective way. Since this involves optimization of the... 

The Sentinel method is the outstanding exponent of the group of interpretive methods, as it has already been applied successfully for selectivity optimization in programmed solvent LC. However, other interpretive methods, based either on fixed experimental designs or on iterative procedures, can be applied along the same lines. It was seen in section 6.3.2.3 that the extension of the Sentinel method to incorporate gradient optimization was fairly straightforward. 

Solvent selection, as such, requires not only knowledge of solution behavior, but also of environmental regulations, solvent viscosity, flash point, odor, etc. Most major solvent suppliers and many larger companies have computer programs to help find optimum solvents. Cohesion energy parameter calculations based on the equations above are central in programs dealing with solvent selection."... 

In the second program, constraints such as compliance with Rule 66, minimum values of the solution parameters, 90% evaporation time, and maximum value of neat viscosity are imposed on the selection of replacement formulas. This second program is a linear optimization program that selects a single solvent blend from a chosen list of... 

Solvent extraction is a technique which has been highly developed within many national nuclear energy programs because of its suitability as a selective separation process for fission products, actinides, and other radioactive substances. The technique is briefly describ in several sections of this book ( 5.5.3,9.2.6,9.4.3,15.7.4,16.3.3,21.7, and especially in 21.6 on the Purex process). It is based on the formation of uncharged organic metal complexes which are preferentially soluble in organic solvents. The three main types of such con unds are ... 

Liquid-liquid extraction (LLE) is a versatile unit operation which may be used for many q>plicaiions. Some examples include the recovery of a solute from a raffinate phase, treaimem of a wadi stream for secondary solute recovery, and the decontamination of wastewaters. In many applications, die solvem selection is a design variable and this choice remains largely a matter of trial and error. Althong predictive techniques are available, there is really no substitute fora strong experimental program in scieenii solvents. 

Figure 6 AMD 2 with a syringe (8) via the motorized valve (1) the selected portions of solvent are taken from the storage bottles (15) and delivered to the chamber (9). When the mobile phase has reached the programmed height on the plate (10) the chamber is drained into the waste bottle (16) and the plate is dried by vacuum from a pump (18). Vacuum is released through conditioning bottles (6, 7) allowing adjustments to the gas phase in the chamber, (photograph courtesy of CAMAG.)...

This section allows the user to calculate the RED fraction from the Hansen solubility parameters for a selected polymer and a mixture of up to three solvents. If three solvents are selected the program calculates and displays the RED for each solvent, the best RED and mixture formulation for every combination of two of the three solvents, and the best RED and mixture formulation for a mixture of all three solvents. The results are displayed in a results window. 

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