Normal phase chromatography summary

In summary, for the chromatographic resolution of sterols it is advisable that reversed phase techniques should be tried initially and in the event of co-elution normal phase chromatography on silica should be tried as an alternative option. For very specific separations where the aforementioned techniques have failed, either NARP or argentation chromatography could be attempted although it is probable that if reversed phase or normal phase failed to elicit a separation, the remaining techniques would also be unsuccessful. 

The separation of positional isomers, i.e., P- and y-tocopherol and to a lesser extent 5,7-dimethyltocol, has been addressed above in different paragraphs. In summary, a complete resolution of P- and y-tocopherol can be achieved by normal-phase chromatography on silica, as well as on diol, amino, and aminocyano bonded phases (Table 3). The three positional isomers have been separated on... 

Fig. 3.1c. Summary of characteristics of normal and reverse phase chromatography...

In summary, an effective resolution of even the most complex mixtures of steroids may be achieved by using a combination of normal and reversed phase chromatography. 

The setnp for polymer HPLC is qnite similar to SEC systems with a few modifications. Liqnid Adsorption Chromatography (LAC) requires the adsorption and desorption on a stationary phase. Therefore, in most cases isocratic separation is not sufficient. Gradients with respect to pH valne, ionic strength, eluent composition, or temperature are applied. The most common approach is to use eluent composition gradients. In contrast to SEC where polymeric phases dominate, silica-based column packings are the most important stationary phase. Both normal phase and reversed phase separations have been described. A summary of different applications in copolymer separation is offered by Pasch [27]. Detectors used in gradient LAC are mainly UV/DAD detectors and ELSD. 

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