Phase separation theoretical background

Although the phase separation of the casting solution has been known by many Investigators to be a necessary process In membrane formation (3-2.), no one has successfully quantitatively described the role of phase separation In the pore forming process In connection with the pore characteristics of the resultant membrane. Theoretical Background... 

The theoretical background for separations up to 3000 bar was discussed comprehensively by Martin and Guiochon.It seems that various phenomena such as the compressibility of the mobile phase or thermal effects occur at pressures above 1000 bar, making it difficult to develop and optimize separations in this region. 

The main principles of separation are adsorption (electrostatic forces), partition (solubility), and ion exchange (charge). Information on the theoretical background of TLC is presented elsewhere (Miller 2004). Depending on the movement of the mobile phase, TLC may be ascending or descending in the nuclear medicine laboratory, ascending TLC is the method of choice (Robbins 1983). 

In other cases, the use of solvent mixtures could influence which diasteieoisomer can be found in the crystalline phase. In such cases, either the crystallizing diasteieoisomer or the one remained in the mother liquor form stable solvate with one of the solvents. After a short summaiy of the theoretical background, it will be shown via examples, how can we use the influence of pH, solvent polarity, and solvate formation, respectively, to imptrove the efficiency of enantiomeric separation. 

Stationary phase The broad spectrum of commercially available columns is a great blessing and also a plague. For some rules and some theoretical background for the selection of RP columns, see Chapter 2.1. In this context, the doublecolumn technique should be mentioned. An example of this is as follows the separation of five quite polar components on a Nucleosil Cjg column is not especially good see Fig. 11. On a CN column, the separation is even worse (see Fig. 12). However, when the two columns are connected in series, a very nice separation under identical, constant conditions is obtained (see Fig. 13). 

The selection of the counter-ion and its concentration are important for the separation of ionic compounds in reversed-phase and ion-exchange liquid chromatography. The addition of hydrophobic ions is an especially powerful method and several surfactants can be used as hydrophobic counter-ions. The theoretical column efficiency of ion-pair liquid chromatography is much better than that of an ion-exchange column, and the regeneration of a column is much faster. Thus, if we can control ion-pair liquid chromatography, we can solve a separation problem. (The important background sources in this area are listed at the end of the chapter.)... 

The fundamentality of the demand for completion of all reactions is saliently elucidated within the background of these simple estimations on the theoretical result of a solid phase synthesis. It is obviously impossible to separate about 84,165 million extremely similar peptidic by-products — whose molecular weights do not differ by more than five amino acid residues of weight - from the main sequence by any presently available method of purification. 

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