Solvent preparative chromatography

Large quantities of solvents are employed for sample preparation, in particular, and these are then concentrated down to a few milliliters. So particularly high quality materials that are as free as possible from residual water and especially free from nonvolatile or not readily volatile impurities ought to be employed here such impurities are enriched on concentration and can lead to gross contamination. The same considerations also apply to preparative chromatography. Special solvents of particular purity are now available. 

There are many advantages of the SMB technology compared to batch preparative chromatography. The process is continuous and the solvent requirement is minimal compared to batch. In SMB, the whole stationary phase is used for the separation while in batch chromatography only a small part of the column is involved in the separation. This allows optimization of productivity with respect to the stationary phase. 

Developing an isolation approach is an activity that is frequently overlooked or addressed as an afterthought. However, solubility and stability data may dictate the development of a chromatographic method that requires the elaboration of the isolation, that is, it is more complicated than a simple evaporation of the mobile phase. The development of the chromatographic process should be linked to and interactively codeveloped with the isolation. Ideally, the isolated impurity sample should not contain other compounds or artifacts, such as solvents, mobile-phase additives or particulate matter from the preparative chromatography, as they may interfere with the structure elucidation effort or adversely affect the stability of the impurity during the isolation process. Therefore, it is preferable to avoid or minimize the use of mobile-phase additives. However, should this prove to be impossible, the additive used should be easy to remove. The judicious choice of mobile phase in the HPLC process increases the ability to recover the compound of interest without or with minimum degradation. The most common... 

In preparative chromatography, the information provided by the isotherms and by the proper model of chromatography will help the scale-up and optimization of batch and continuous purifications with minimum use of solvents and sample. Although it is rather difficult to give straightforward instructions how to optimize a preparative separation, some general guidelines are provided in this chapter. 

Purification by preparative HPLC is accomplished as follows. The crude product is taken up in 60 mL of 4 1 hexanes-ethyl acetate. The solution is subjected to preparative HPLC (Note 24) using the same solvent system. Chromatography 1s monitored by TLC (Note 26) and the appropriate fractions are combined. Solvent removal with a rotary evaporator at 35 C (12 mm) gives a colorless oil. This material is subjected to bulb-to-bulb distillation at 75-90°C (8 am). 

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