Solvents enantiomer separation with

Thus far, the most successful approach to M IP-based CEC utilises capillary columns filled with a monolithic, super-porous imprinted polymer [39-41]. The morphology of a certain MIP monolith is depicted in Fig. 16.3. Using this system enantiomer separations with baseline resolution have been carried out in less than 2 minutes. The M IP-filled capillaries are obtained by an in situ photo-initiated polymerisation process (Fig. 16.4]. The capillary is filled with a pre-polymerisation mixture of imprint molecule, functional and cross-linking monomers (MAA and TRIM, respectively), radical initiator (2,2 -azobisisobutyronitrile) and solvent (toulene). Both ends of the capillary are sealed and the polymerisation is performed... 

Enantiomer separation factors (a values) for valine and phenylalanine as well as their esters of 5-10 for phenylalanine and 4-10 for valine have been shown at the 0.1-1 g ChiraLig scale. These a values vary as a function of solvent and other loading matrix factors (pH, salts, etc.). However, all of these cases show a values high enough to obtain reasonable enantiometric purity in less than or equal to three stages. The system with a value of = 6 for the valine methyl ester enantiomers has the ability to load the valine onto the resin in H,0 containing LiClO and also to... 

A simple and rapid method of separating optical isomers of amino acids on a reversed-phase plate, without using impregnated plates or a chiral mobile phase, was described by Nagata et al. [27]. Amino acids were derivatized with /-fluoro-2,4-dinitrophenyl-5-L-alanine amide (FDAA or Marfey s reagent). Each FDAA amino acid can be separated from the others by two-dimensional elution. Separation of L- and D-serine was achieved with 30% of acetonitrile solvent. The enantiomers of threonine, proline, and alanine were separated with 35% of acetonitrile solvent and those of methionine, valine, phenylalanine, and leucine with 40% of acetonitrile solvent. The spots were scraped off the plate after the... 

Immobilized Chirasil-Dex phases are resistant to stationary phase bleeding, compatible with solvent input and are insensitive to temperature shock. The immobilization of Chirasil-Dex was a prerequisite for extending the scope of enantiomer separation to involatile racemates using supercritical fluid chromatography130 and was utilized in the separation of 7-chloro-2,3,4,5-te-trahydro-l-methyl-5-phenyl-l, 4-benzodiazepin-2(l//)-one (dihydrodiazepam) (Figure 17). 

In membrane extraction, the treated solution and the extractant/solvent are separated from each other by means of a solid or liquid membrane. The technique is applied primarily in three areas wastewater treatment (e.g., removal of pollutants or recovery of trace components), biotechnology (e.g., removal of products from fermentation broths or separation of enantiomers), and analytical chemistry (e.g., online monitoring of pollutant concentrations in wastewater). Figure 18a shows schematically an industrial hollow fiber-based pertraction unit for water treatment, according to the TNO technology (263). The unit can be integrated with a him evaporator to enable the release of pollutants in pure form (Figure 18b). 

Peters et al. reported on rod-CEC on a chiral monolith [50] which was prepared by copolymerization of the chiral monomer 2-hydroxyethyl methacrylate (A -L-valine-3,5-dimethylanilide) carbamate with ethylene dimethylacrylate, 2-acrylamido-2-methyl-l-propanesulfonic acid and butyl or glycidyl methacrylate in the presence of a porogenic solvent. The electrochromatographic enantiomer separation of 7V-(3,5-dinitrobenzoyl)leucine diallylamide was feasible at 25 kV the inlet and outlet buffer vials were both pressurized. 

It also needs to be emphasized that it was the development of robust and broadly applicable CSPs that has laid the foundations for economic chromatographic enantiomer separation on a preparative scale. Although indirect [57-62] and CMPA-based direct [63-65] chromatographic methodologies have seen some use in preparative enantiomer separation, the considerable efforts associated with chemical manipulation and/or recovery of the products render these approaches economically unattractive [66]. Preparative enantiomer separations employing CSPs are not subject to these limitations. With CSPs enantiomers can be processed directly (i.e. without prior derivatization) with readily volatile achiral mobile phases (devoid of SOs), simplifying product recovery to a trivial solvent evaporation step. 

Host-guest inclusion complexations are usually carried out in organic solvents. As a green process, inclusion complexation can be performed in a water suspension medium or in the solid state. When the solid-state reaction in a water suspension medium is combined with an enantioselective inclusion complexation in the same water medium, a one-pot green preparative method for obtaining optically active compounds can be designed. In all these cases, enantiomers separated as inclusion complexes are recovered by distillation of the inclusion complex. When enantioselective inclusion complexation in the solid state is combined with the distillation technique, a unique green process for enantiomeric separation can result. 

Matsui et al. [162] first reported the preparation of molecularly imprinted monoliths based on functional monomer such as methacrylic acid or 2-trifluoromethyl-acrylic acid via in situ polymerization. The reaction mixture consisting of monomer, cross-linker (ethylene glycol dimethacrylate), porogenic solvents (cyclohexanol and 1-dodecanol), initiator, and template molecule was degassed and poured into a column where the polymerization took place. When reaction is completed, the template molecule and the porogenic solvents were extracted with methanol and acetic acid resulting in monoliths with molecular recognition in the separation of positional isomers of diaminonaphthalene and phenylalanine anilide enantiomers. 

The three protein stationary phases behave very similarly, in that retention and chiral selectivity is controlled by pH and the concentration of solvent in the mobile phase. However, the selectivity for a given enantiomer pair can be very different on each stationary phase despite the fact that they are all protein based. This is demonstrated in figure 8.3. The retention of the enantiomers of Talinolol and Atenolol decrease with increase in 2-propanol in the mobile phase which, if largely retained by dispersive interactions, would be expected. However, the chiral selectivity oi the stationary phase to the two pairs of enantiomers of the stationary phase to the two pairs of enantiomers increases with the 2-propanol content of the mobile phase. This would indicate that the chiral selectivity was more likely to be due to polar interactions. However, it is interesting to note that although the retention of Kynurenine also falls with increase 2-propanol concentration, when separated on the CHIRAL-HSA phase, the chiral selectivity also /fa. 

Exactly the same process takes place as that in the Hurrel system but, in effect, the valving makes the columns appear to move instead of the packing. Part of the feed moves with the mobile phase and is collected by a small take-off flow in front of the feed port (B + solvent). The other, more retained portion of the sample, accumulates in a column on the other side of the feed port and is collected by a another small take-off flow behind the feed port (A + solvent). This particular system ideally, produces two products and thus lends itself specifically to the separation of enantiomeric pairs. However, for effective separation with high purity yields, the stationary phase capacity for the two enantiomers must be fairly large and thus the phase system must be carefully selected. The technique has been successfully used to isolate single enantiomer drugs [15-17]. 

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