Batch elution modes, chromatography

At the current time, there is considerable interest in the preparative applications of liquid chromatography. In order to enhance the chromatographic process, attention is now focused on the choice of the operating mode [22]. SMB offers an alternative to classical processes (batch elution chromatography) in order to minimize solvent consumption and to maximize productivity where expensive stationary phases are used. 

In a series of papers by Vigh and co-workers [143-145], it has been shown that displacement chromatography may allow micropreparative (1 mg) separations of enantiomers to be performed with somewhat better chemical and enantiomeric recoveries than in the overloaded elution mode. However, this technique does not offer principal solutions to the above-mentioned inherent problems of the elution batch mode, and is not discussed in detail here. 

The three main modes of chromatographic operation are elution chromatography, selective adsorption/desorption, and simulated countercurrent chromatography. Of these, elution chromatography, used as a cyclic batch process, was the first to be developed for large-scale separations. 

Chromatography of material such as proteins has occasionally been carried out in batch mode. Here the proteins are adsorbed onto a chromatographic medium by mixing the sample and the media in a common vessel prior to specific elution of the various adsorbed proteins. The mixture s components are subsequently eluted from the media by various types of elution schemes (e.g., salt and/or pH steps or gradients, specific affinity elution, etc.). 

Chromatographic Techniques. These techniques have long been applied to the problems of separation and analysis of trace atmospheric species. For stable species, batch samples are usually collected as described in the preceding section and transported to the laboratory for subsequent analysis. However, some compounds are not sufficiently stable to survive transport intact. In situ chromatographic analyses have been used for these samples. Usually, chromatography is used on aircraft in a batch mode samples are collected, preconcentrated, and separated on a column, and the individual species are detected as they elute the process is then repeated for the next sample. Thus, as with other batch techniques, time resolution is limited. 

An alternative approach is the technique of suspended bed chromatography. Here, ion exchangers and columns designed for packed bed operations may be used in alternative protocols. Briefly, adsorption is carried out in batch mode, and the resulting adsorbent suspension is filter collected/clarified in a conventional fixed bed contactor for washing and elution. This approach is enabled by the availability of pump-packed column chromatography systems. The technique was first demonstrated with a clarified... 

Isocratic elution is preferable in batch mode for the separation of closely related analytes to enhance selectivity and allow automation and short injection cycle. Automated injections provide an opportunity for repetitive unattended operation. In isocratic separations, sample injection is often done before the previously injected product elutes from the column, thus reducing cycle time and solvent consumption (Fig. 2). This technique is especially useful in chiral chromatography, where automated processes are used to decrease the required amount of expensive stationary phases, lowering the overall separation expenses. 

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