Direct separation

AGP columns have wide appHcation for the direct separation of enantiomers of many different classes of dmgs, amines, acids, and nonprotolytic compounds (18,23). Acidic dmgs resolved include ibuprofen [15687-27-17, C 2H g02, ketoprofen [22071 -15 ] and naproxen [22204-53-17,... 

A. Walhagen and F.-E. Edholm, Coupled-column cliromatography of immobilized protein phases for direct separation and determination of dmg enantiomers in plasma , 7. Chromatogr. 473 371-379 (1989). 

For the separation of racemic mixtures, two basic types of membrane processes can be distinguished a direct separation using an enantioselective membrane, or separation in which a nonselective membrane assists an enantioselective process [5]. The most direct method is to apply enantioselective membranes, thus allowing selective transport of one of the enantiomers of a racemic mixture. These membranes can either be a dense polymer or a liquid. In the latter case, the membrane liquid can be chiral, or may contain a chiral additive (carrier). Nonselective membranes can also... 

Cytokinesis is the separation of daughter cells at the completion of the microtubule directed separation of duplicate chromosomes at mitosis or meiosis. This is usually accomplished by a purse string mechanism, whereby daughter cells become separated by the gradual constriction of a structure composed of actin microfilaments and myosins-II (Fujiwara and Pollard, 1976 Satterwhite and Pollard, 1992). 

K well-ordered chains running in the < 110 > direction separated by the atom resolved structure of the Cu(l 10) surface with a spacing between the rows of 0.36 nm (see line profile), (b) The spacing within the chains is 0.51 nm (see line profile), i.e. close to twice the Cu-Cu distance within the copper rows running in the < 110 > direction. (Reproduced from Refs. 16, 18). 

Major applications of modern TLC comprise various sample types biomedical, pharmaceutical, forensic, clinical, biological, environmental and industrial (product uniformity, impurity determination, surfactants, synthetic dyes) the technique is also frequently used in food science (some 10% of published papers) [446], Although polymer/additive analysis takes up a small share, it is apparent from deformulation schemes presented in Chapter 2 that (HP)TLC plays an appreciable role in industrial problem solving even though this is not reflected in a flood of scientific papers. TLC is not only useful for polymer additive extracts but in particular for direct separations based on dissolutions. 

Our main motivation to develop the specific transient technique of wavefront analysis, presented in detail in (21, 22, 5), was to make feasible the direct separation and direct measurements of individual relaxation steps. As we will show this objective is feasible, because the elements of this technique correspond to integral (therefore amplified) effects of the initial rate, the initial acceleration and the differential accumulative effect. Unfortunately the implication of the space coordinate makes the general mathematical analysis of the transient responses cumbersome, particularly if one has to take into account the axial dispersion effects. But we will show that the mathematical analysis of the fastest wavefront which only will be considered here, is straight forward, because it is limited to ordinary differential equations dispersion effects are important only for large residence times of wavefronts in the system, i.e. for slow waves. We naturally recognize that this technique requires an additional experimental and theoretical effort, but we believe that it is an effective technique for the study of catalysis under technical operating conditions, where the micro- as well as the macrorelaxations above mentioned are equally important. 

One of the most powerful methods for determining enantiomer composition is gas or liquid chromatography, as it allows direct separation of the enantiomers of a chiral substance. Early chromatographic methods required the conversion of an enantiomeric mixture to a diastereomeric mixture, followed by analysis of the mixture by either GC or HPLC. A more convenient chromatographic approach for determining enantiomer compositions involves the application of a chiral environment without derivatization of the enantiomer mixture. Such a separation may be achieved using a chiral solvent as the mobile phase, but applications are limited because the method consumes large quantities of costly chiral solvents. The direct separation of enantiomers on a chiral stationary phase has been used extensively for the determination of enantiomer composition. Materials for the chiral stationary phase are commercially available for both GC and HPLC. 

Kroodsma (6) studied the use of a filter to separate the urine and the faeces. The main target is to transport the mixture of faeces and some straw to arable farmers and spread the urine on own farmland. But a side effect of direct separation is a reduction of the emission of odours. This separation system is relative expensive, especially in modem pighouses with transverse channels. For a 500-pig unit the extra investment is at least Dfl. 70,- per pig place. The total annual costs are Dfl. 5,- per pig place. In a pighouse with channels in length this system is cheaper and this difference increases when the house is longer. 

Direct and indirect chromatographic methods were developed and compared in systematic examinations for the enantioseparation of P-amino acids direct separation of underivatized analytes involved the use of commercially available Crownpak CR(-I-), teicoplanin, and ristocetin A CSPs [148], while indirect separation was based on precolumn derivatization with 2,3,4,6-tetra-G-acetyl-f)-D-glucopyranosyl isothiocyanate (GITC) or A - a-(2,4-dinitro-5-fluorophenyl)-L-alaninamide (EDAA, Marfey s reagent), with subsequent separation on a nonenantioselective column. 

Owens, P.K., Svensson, L.A., and Vessman, J., Direct separation of captoprU diastereoisomers including their rotational isomers by RP-LC using a teicoplanin column, 7. Pharm. Biomed. Anal, 25, 453, 2001. 

By adding a chiral molecule to the mobile phase, the direct separation of enantiomers can be obtained on an achiral stationary phase. This... 

One of the most sophisticated methods is the use of chiral gas chromatographic capillary columns for the direct separation of volatile enantiomers. Complexation gas chromatography with enantioselec-tive transition metal fl-ketoenolates permits the stereochemical analysis of volatile oxygenated compounds in the nanogram range with high 44,45... 

Quantitation of synthetic, conjugated bilirubin, after its direct separation from the incubation mixtures, offers the most valid approach to the determination of conjugation rates. However, for the present, such methods are unlikely to find wide application because of instability of... 

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