Separator cyclodextrin-bonded phases

Cyclodextrin stationary phases utilize cyclodextrins bound to a soHd support in such a way that the cyclodextrin is free to interact with solutes in solution. These bonded phases consist of cyclodextrin molecules linked to siUca gel by specific nonhydrolytic silane linkages (5,6). This stable cyclodextrin bonded phase is sold commercially under the trade name Cyclobond (Advanced Separation Technologies, Whippany, New Jersey). The vast majority of all reported hplc separations on CD-bonded phases utilize this media which was also the first chiral stationary phase (csp) developed for use in the reversed-phase mode. 

Appllca.tlons. The first widely appHcable Ic separation of enantiomeric metallocene compounds was demonstrated on P-CD bonded-phase columns. Thirteen enantiomeric derivatives of ferrocene, mthenocene, and osmocene were resolved (7). Retention data for several of these compounds are listed in Table 2, and Figure 2a shows the Ic separation of three metallocene enantiomeric pairs. P-Cyclodextrin bonded phases were used to resolve several racemic and diastereomeric 2,2-binaphthyldiyl crown ethers (9). These compounds do not contain a chiral carbon but stiU exist as enantiomers because of the staggered position of adjacent naphthyl rings, and a high degree of chiral recognition was attained for most of these compounds (9). 

The more useful types of chirally active bonded phases are those based on the cyclodextrins. There are a number of different types available, some of which have both dispersive or polar groups bonded close to the chirally active sites to permit mixed interactions to occur. This emphasizes the basic entropic differences between the two isomers being separated. A range of such products is available from ASTEC Inc. and a separation of the d and / isomers of scopolamine and phenylephrine are shown in figure 4. The separations were carried out on a cyclodextrin bonded phase (CYCLOBOND 1 Ac) that had been acetylated to provide semi-polar interacting groups in close proximity to the chiral centers of the cyclodextrin. The column was 25 cm long, 4.6 mm in diameter and packed with silica based spherical bonded phase particles 5pm in diameter. Most of the columns supplied by ASTEC Inc. have these dimensions and, consequently, provide a... 

The Separation of the Isomers of Scopolamine and Phenylephrine on a Cyclodextrin Bonded Phase... 

It is seen that, providing the isomers are eluted at a (kf) value greater than about 2.0, the column will separate those solute pairs having separation ratios as low as about 1.03. This, however, assumes that the column is very well packed and is operated at about the optimum mobile phase velocity. In practice, a more realistic minimum separation ratio would be between 1.035 and 1.04. However, as it will be seen, the cyclodextrin bonded phases can easily provide separation ratios significantly greater than these values. This is achieved by... 

Armstrong, D.W. and DeMond, W., Cyclodextrin bonded phases for the liquid chromatographic separation of optical, geometrical, and structural isomers, J. Chromatogr. Sci., 22, 411, 1984. 

Chiral stationary phase 138 Covalently attached /3-cyclodextrin bonded phase exploratory separations of PITC-, dansyl-, dabsyl-, and AQC-derivatized amino acids... 

Han SM, Armstrong DW, HPLC separation of enantiomers and other isomers with cyclodextrin bonded phases rule for chiral recognition, in Chiral Separations by HPLC (Krstulovic AM, Ed.), Ellis Horwood, Chichester, p. 208 (1989). 

A Guide to Using Cyclodextrin Bonded Phases for Liquid Chromatography, Advanced Separation Technologies, Inc., Whippany, NJ (1996). 

Cyclobond Handbook A Guide to Understanding Cyclodextrin Bonded Phases for Chiral LC Separations, 6th ed., Advanced Separation Technologies, Wippany, NJ, 2002. 

Armstrong, D.W., DeMond, W., and Czech, B.P., Separation of metallocene enantiomers by liquid chromatography chiral recognition via cyclodextrin bonded phases, Anal. Chem., 57, 481, 1985. 

Chang, C.A., Wu, Q., and Tan, L., Normal-phase high-performance liquid chromatographic separations of positional isomers of substituted benzoic acids with amine and P-cyclodextrin bonded-phase columns, J. Chromatogr., 361, 199, 1986. 

T. J. Ward and D. W. Armstrong, Cyclodextrin bonded phases. In Chromatographic Chiral Separations (M. Zief and L. Crane ed.), Marcel Dekker, Inc., New York, 1987. 

TABLE 4 Separation Data for Enantiomeric Compounds Using a 10-cm P-Cyclodextrin Bonded Phase Column 1... 

A special cyclodextrin bonded phase, with an appropriate binder, has been used in TLC plates to separate isomers, including optical isomers.45 Another type of TLC plate made by Macherey-Nagel uses a reverse phase bonded layer with Cu2+ ions and an unspecified chiral reagent. 

With chiral stationary phases, chromatographic separation of enantiomeric ferrocene derivatives is possible. An apparatus for the resolution of ferrocenyl alcohols and other compounds on triacetylcellulose has been described [60]. Analytical enantiomer separation of ferrocenyl alcohols, ethers, sulfides, and amines for the determination of enantiomeric excesses is best achieved on cyclodextrin bonded phases [61]. 

Piperaki, S. Perakis, A. Parissi-Poulou, M. Liquid chromatographic retention behaviour and separation of promethazine and isopromethazine on p-cyclodextrin bonded-phase column. J.ChromatogrA, 1994,... 

The conventional C-18 and the CD columns do interact differently with solutes of certain classes of isomers. For example, C-18 columns cannot separate enantiomers unless special additives are introduced into the mobile phase. The cyclodextrin bonded phases, however, can easily separate enantiomeric species as illustrated in Figure 9. The D and L enantiomers of dansyl-DL-leucine and of dansyl-DL-norleucine are resolved using a beta-CD column, but attempts to separate these isomers were unsuccessful using a C-18 column. The nature of the interactions between enantiomers and the cyclodextrin cavity has been described elsewhere (20. 21). 

The cyclodextrin based chiral stationary phases are some of the more popular materials used for contemporary chiral separations. One of their distinct advantages lies in their unrestricted and successful use with all types of solvent. In particular, they can be used very effectively in the reversed phase mode (a method of development that is not possible with some other chiral stationary phases) and, as well as being usable in a normal phase. They can also be used in the so-called polar organic mode, where the polar constituents of the mobile phase can be anhydrous diethylamine or glacial acetic acid, but in the complete absence of water. The cyclodextrins and their derivatives are widely used for all types of chiral separations, they have a good sample capacity, and can often be used for preparative separations. Cyclodextrin-based phases are readily available, usually covalently bonded to spherical silica gel particles 5 pm in diameter. There are numerous examples of the use of cyclodextrins in chiral separations and the following are some applications that illustrate their general use. 

D.W. Armstrong and W. DeMond, Cyclodextrin Bonded Phases for the Liquid Chromatographic Separation of Optical, Geometrical, and Structural Isomers, J. Chromatog. Sci., 22(1984)411. 

D.W. Armstrong, W. DeMond, and B.P. Czech, Separation of Metallocene Enantiomers by Liquid Chromatography Chiral Recognition via Cyclodextrin Bonded Phases, Anal. Chem., 57(1985)481. 

D.W. Armstrong, A. Alak, W. DeMond, W.L. Hinze and T.E. Riehl, Separation of Mycotoxins, Polycyclic Aromatic Hydrocarbons, Quinones, and Heterocyclic Compounds on Cyclodextrin Bonded Phases An Alternative LC Packing, J. Liq. Chromatogr., 8(2)(1985)261. 

C.A. Chang, Q. Wu and D.W. Armstrong, Reversed Phase HPLC, Chromatographic Separation of Substituted Phenolic Compounds with a P-Cyclodextrin Bonded Phase Column, J. Chromatogr., 354 (1986)454. 

D.W. Armstrong and W. Li, Optimization of Liquid Chromatographic Separations on Cyclodextrin Bonded Phases, Chromatography, March(1987)43. 

D.W. Armstrong, X. Yang, S.M. Han and R.A. Menges, Direct Liquid Chromatographic Separation of Racemates with an a-Cyclodextrin Bonded Phase, Anal. Chem., 59(1987)2594. 

C.A. Chang and Q. Wu, Facile Liquid Chromatographic Separation of Positional Isomers with a y-Cyclodextrin Bonded Phase Column, J. Liq. Chromatogr., 10(7)(1987)1359. 

C.A. Chang and Q. Wu, Comparison of Liquid Chromatographic Separations of Geometrical Isomers of Substituted Phenols with P- and y- Cyclodextrin Bonded Phases, Anal. Chim. Acta, 189 (1986)293. 

S.M. Han, Y.I. Han and D.W. Armstrong, Structural Factors Affecting Chiral Recognition and Separation on P-Cyclodextrin Bonded Phases, J. Chromatogr., 441(1988)376. 

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