Chiral stationary phases liquid

If a chiral liquid is coated on the surface of the column packing particles, a chiral liquid-liquid partition system is obtained. The mobile phase must be saturated with stationary phase. A thermostat must be provided in order to keep 

---

The use of a chiral liquid stationary phase. The packing of an LC column, e.g., silica, is coated with a film of a liquid, optically pure compound that must not be soluble in the mobile phase used. A possible phase pair is a tartrate derivative in combination with an aqueous buffer eluent. The handling of such liquid-liquid chromatographic systems is not simple, which is why they are not often used, and they are... 

Alain Berthod received his PhD in 1979 from the University of Lyon. He took an assistant professor s position at the French National Center for Scientific Research (CNRS) working in electrochemistry. In 1983 he was promoted as associate professor and in 1993 as research director. He focused on the developing and the use of micellar solutions and microemulsions in chromatography. His interests lie in the separation of chiral molecules and enantiorecognition mechanisms. He has contributed to the development of the countercurrent chromatography technique that uses a sup-port-free liquid stationary phase. He was member of the editorial board of major analytical chemistry and chromatography journals. He is editor-in-chief of Separation Purification Reviews (Taylor Francis, Philadelphia, Pennsylvania). 

Countercurrent chromatography (CCC) can be used for the separation of a variety of enantiomers by adding a chiral selector to the liquid stationary phase [1,2], The method is free of complications arising from the use of a solid support and also eliminates the procedure of chemically bonding the chiral selector to a solid support as in conventional chiral chromatography. 

The use of this isotherm model is justified by the existence of a bimodal energy distribution on the adsorbent surface [34r-36]. It accounts well for many adsorption systems in reversed phase liquid chromatography and for isotherm data obtained with numerous chiral selective stationary phases [36]. The profiles obtained with this isotherm exhibit a long tail at the end of the large concentration band (see Figure 7.6b,d). 

Table 10.8 Covalently bonded synthetic low-molecular mass chiral selector stationary phases for liquid chromatography ...

Analogous to liquid chromatography, CCC can be used for chiral separation by dissolving the chiral selector in the liquid stationary phase. The method has some advantages over liquid chromatography in that the amount of the chiral selector in the column can be much greater (since it is dissolved in the stationary phase) and the same column may be used for various kinds of chiral separations simply by changing the chiral selector in the stationary phase. 

Normal-phase HPLC usually offers much improved separation of positional isomers or stereoisomers with respect to RPLC. This is also the reason why normal-phase liquid chromatographic mode with nonaqueous mobile phases is often used for the separation of enantiomers on chiral bonded stationary phases. 

Countercurrent chromatography can be applied to the separation of enantiomers by adding a suitable chiral selector to the liquid stationary phase by analogy to binding the... 

Abstract Countercurrent chromatography (CCC) is a preparative separation technique that works with a liquid stationary phase. Biphasic liquid systems are needed to perform a separation. Since a chiral selector is required to perform enantiomer separations, special requirements are imposed in CCC. The chiral selector (CS) must be located in the stationary phase since partitioning with the mobile phase would cause losses of the valuable chiral selector in the mobile phase. Sulfated cyclodextrins and proteins were used as polar CS located in the polar stationary phase (reversed phase mode). Apolar CSs such as A-dodecyl-L-proline... 

Regarding to the separation of enantiomers, the preparative application of CCC can be of great interest since this technique offers the possibility to produce enan-tiomerically pure compounds at a lower cost compared to conventional liquid chromatography. As for other enantioselective separation techniques, in CCC, a chiral selector (CS) is needed. To produce the enantioselective environment able to separate enantiomers, it is preferably added to the liquid stationary phase. The chiral selector is designed to be confined in the stationary phase thanks to its solubility properties, while the racemate is partitioned between the two phases of the biphasic solvent system. Moreover, the CS must preserve its enantioselectiv-ity in the biphasic liquid chosen. Encountering a combination of solvent system/CS, adapted to the analyte under study, which fulfill the specified requirements is not an easy task. This is the main reason for the few publications released in this field [20, 21]. 

High Performance Liquid Chromatography. Although chiral mobile phase additives have been used in high performance Hquid chromatography (hplc), the large amounts of solvent, thus chiral mobile phase additive, required to pre-equiUbrate the stationary phase renders this approach much less attractive than for dc and is not discussed here. 

F W. Wainer and R. M. Stifhn, Direct resolution of the stereoisomers of leucovorin and 5-methylteti ahydrofolate using a bovine serum albumin liigh-performance liquid cliromatographic chiral stationary phase coupled to an acliiral phenyl column , 7. Chromatogr. 424 158-162 (1988). 

HPLC separations are one of the most important fields in the preparative resolution of enantiomers. The instrumentation improvements and the increasing choice of commercially available chiral stationary phases (CSPs) are some of the main reasons for the present significance of chromatographic resolutions at large-scale by HPLC. Proof of this interest can be seen in several reviews, and many chapters have in the past few years dealt with preparative applications of HPLC in the resolution of chiral compounds [19-23]. However, liquid chromatography has the attribute of being a batch technique and therefore is not totally convenient for production-scale, where continuous techniques are preferred by far. 

W. H. Pirkle and B. C. Hamper, The direct preparative resolution of enantiomers by liquid chromatography on chiral stationary phases in Preparative Liquid Chromatography, B. A. Bidling-meyer (Ed.), Journal Chromatography Library Vol. 38, 3 Edition, Elsevier Science Publishers B. V, Amsterdam (1991) Chapter 7. 

A. M. Stalcup, Cyclodextrin bonded chiral stationary phases in enantiomer separations in A practical approach to chiral separations by liquid chromatogra.phy, G. Subramanian, VCH, Weinheim (1994) Chapter 5. 

Despite the difficulties caused by the rapidly expanding literature, the use of chiral stationary phases (CSPs) as the method of choice for analysis or preparation of enantiomers is today well established and has become almost routine. It results from the development of chiral chromatographic methods that more than 1000 chiral stationary phases exemplified by several thousands of enantiomer separations have been described for high-performance liquid chromatography (HPLC). 

The versatility of chiral stationary phases and its effecitve application in both analytical and large-scale enantioseparation has been discussed in the earlier book A Practical Approach to Chiral Separation by Liquid Chromatography" (Ed. G. Sub-ramanian, VCH 1994). This book aims to bring to the forefront the current development and sucessful application chiral separation techniques, thereby providing an insight to researchers, analytical and industrial chemists, allowing a choice of methodology from the entire spectrum of available techniques. 

---