Chromatography straight-phase partition

Chapter 3 through Chapter 8 deal with the basic aspects of the practical uses of PLC. Chapter 3 describes sorbent materials and precoated layers for normal or straight phase (adsorption) chromatography (silica gel and aluminum oxide 60) and partition chromatography (silica gel, aluminum oxide 150, and cellulose), and precoated layers for reversed-phase chromatography (RP-18 or C-18). Properties of the bulk sorbents and precoated layers, a survey of commercial products, and examples of substance classes that can be separated are given. 

In contrast to straight phase or adsorption chromatography, partition chromatography involves the separation of sample molecules owing to their different partition coefficients between the liquid stationary and mobile phases. The liquid stationary phase is located in the pores of a sorbent, ideally only acting as a support, making no contribution to the retention of the sample molecules. 

Aluminum oxides, similar to silica gels, are available as bulk materials and as precoated plates, to be used not only for straight phase adsorption chromatography, but also for partition PLC (see Table 3.3 and Table 3.4). In particular, the aluminum oxide type 150 (i.e., mean pore diameter 150 A [15 tun]) is suitable for partition chromatographic purposes. 

In addition to LH-20, a wide range of other lipophilic Sephadex derivatives has been prepared to improve the flexibility of the gel in organic solvents [219]. For example, hydroxypropylated G-50 was used to characterise a range of oligomeric polyethers [220] and a lipophilic derivative of G-15 was used for the analytical characterisation of pyr-ethrum extracts [221], A chiral derivative of LH-20 was prepared by reaction of the gel with 23,24-oxido-5/3-cholane [222]. The gel formed swelled in both polar and non-polar solvents and its application in both straight-phase and reversed-phase systems was discussed. A hydroxy-cyclohexyl derivative of LH-20, suitable for straight-phase and reverse-phase partition chromatography, has been prepared and evaluated in the separation of various steroids [223]. 

The analysis of quaternary nitrogen compounds by HPLC requires chromatographic systems, such as ion-pair and reversed-phase chromatography, which are able to separate highly polar compounds. Reviews on ion-pair HPLC have been given . Both straight-phase (adsorption and/or partition) and reversed-phase ion-pair chromatography have been used. 

NORMAL-PHASE CHROMATOGRAPHY. Adsorption or partition TLC in which the stationary phase is polar in relation to the mobile phase. Also referred to as straight phase chromatography. 

---