Chromatography, preparative chromatographic

Ruthven, D.M. and Ching, C.B. (1993) Modeling of chromatographic processes. Preparative and production scale chromatography. In Chromatographic Science Series, Vol. 61. Eds. Ganetos, G., Barker,... 

Specificity may be achieved through sample preparation, chromatographic selectivity, the selectivity of the detection method or combinations of these. It is often tempting to utilise the most selective detection method available (such as MS or MS/MS), since this can reduce the effort required in optimising the sample preparation and chromatography. However, whilst this is often the most expedient approach in early development, it may not always be suitable to transfer expensive, highly technical methods and instrumentation into a manufacturing environment if this is required. 

The method of complete electrolysis is also important in elucidating the mechanism of an electrode reaction. Usually, the substance under study is completely electrolyzed at a controlled potential and the products are identified and determined by appropriate methods, such as gas chromatography (GC), high-performance liquid chromatography (HPLC), and capillary electrophoresis. In the GC method, the products are often identified and determined by the standard addition method. If the standard addition method is not applicable, however, other identification/determination techniques such as GC-MS should be used. The HPLC method is convenient when the product is thermally unstable or difficult to vaporize. HPLC instruments equipped with a high-sensitivity UV detector are the most popular, but a more sophisticated system like LC-MS may also be employed. In some cases, the products are separated from the solvent-supporting electrolyte system by such processes as vaporization, extraction and precipitation. If the products need to be collected separately, a preparative chromatographic method is use-... 

Adsorption chromatography. This chromatographic technique is best known because of its use in the last century as a preparative method of separation. Stationary phases have made a lot of progress since Tswett. who used calcium carbonate or sugar. The separation of organic compounds on a thin layer of silica gel or alumina with solvent as a mobile phase are examples of this type of chromatography. Solutes bond to the stationary phase because of physisorption or chemisorption interactions. The physico-chemical parameter involved is the coefficient of adsorption. 

J. Dingenen and J. N. Kinkel, Preparative chromatographic resolution of racemates on chiral stationary phases on laboratory and production scales by closed-loop recycling chromatography , J. Chromatogr. 666 627 -650 (1994). 

Figure 1. Use of analytical chromatography as an on-line species-specific detector for a preparative chromatographic process.

Chromatographic System (See Chromatography, Appendix IIIA.) Set up the system with reference to High-Performance Liquid Chromatography. The chromatograph has a 254-nm detector and a 15-cm x 4.6-mm column that contains 5-to 10-mm porous microparticles of silica bonded to octylsilane (Zorbax 8, or equivalent). Set the flow rate to about 2 mL/ min. Chromatograph three replicate injections of the Standard Preparation, and record the peak responses as directed under Procedure. The relative standard deviation is not more than 2.0%, and the resolution factor between nitrilotriacetic acid and Calcium Disodium EDTA is not less than 4.0. 

B. Apparatus (See Chromatography, Appendix IIA.) Assemble a suitable apparatus for ascending thin-layer chromatography. Prepare a slurry of chromatographic silica gel containing about 13% of calcium sulfate (1 g to each 2 mL of water) as the binder, apply a uniformly thin layer to glass plates of convenient size, dry in air for 10 min, and activate by drying at 100° for 1 h. Store the cool plates in a clean, dry place until ready for use. 

The development of preparative chromatographic processes in fine chemistry and in pharmaceutical industries is a very important field of research. This new process called SF-SMB (Supercritical Fluid Simulated Moving Bed) is a attempt to optimize preparative chromatography by three ways the choice of a supercritical C02 as eluent, the implementation of the simulated moving bed, and the use of an elution strength modulation in the process, performing a pressure gradient. 

Preparative chromatography is a proven technology for the separation of specialty chemicals mainly in food and pharmaceutical industries, particularly the enantioseparation of chiral compounds on chiral stationary phases. The potential of preparative chromatographic systems were further increased by the development of continuous chromatographic processes like the simulated moving bed (SMB) process. Compared to the batch column chromatography, the SMB process offers better performance in terms of productivity and solvent consumption [2]. 

Although chromatography is generally considered to be an analytical tool, it also has an important role in process chemistry as a means of isolating and/or purifying substances from complex or dilute mixtures. Preparative chromatographic methods for the generation of laboratory-scale to commercial-scale quantities of pure substances are well documented in the chemical and patent literature. 

The product was finally identified as 9a-OH-PS by NMR, after isolation by semi-preparative chromatography. A two-step semi-preparative chromatographic separation was run in order to achieve high purity of the sample. First NPLC was performed to get rid of yellow strongly nonpolar compounds from the fermentation medium. The fraction from the NPLC eluate containing the product was further purified using a high resolution RPLC column. 

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