Mobile imprinted chiral phases

Figure 6 Chiral HPLC separation of amino acid derivatives on imprinted stationary phases packed with Z-L-Glu-OH (a), Boc-L-phe-Gly-OEt (b), Z-L-Ala-L-Ala-Ome (c) Z-L-Ala-Gly-L-Phe-OMe (d). Mobile phase chloroform - acetic acid. Column 250 x 4.6 mm. Flow rate, 1 mL/min. Detection, UV 260 nm. Reproduced from Ref. 22, with permission.

Figure 7 Chiral HPLC separation of 2-arylpropionic acid derivatives on nonimprinted (a) and (5)-naproxen-imprinted stationary phase (b). (1) Racemic ketoprofen, (2) racemic ibu-profen, (3) (R)-naproxen, (4) (5)-naproxen. Mobile phase, 20 mM phosphate buffer pH 3.2 -acetonitrile 1 + lv/v. Columns 100 x 4.6 mm. Flow rate, ImL/min. Detection, UV 254 nm. Reproduced from Ref. 45, with permission.

Figure 8 Chiral HPLC separation of a equimolar mixture of (-)-cinchonidine (1) and (+)-cinchonidine (2) on a (—)-cinchonidine-imprinted stationary phase. Mobile phase, methanol -acetic acid 7 + 3 v/v. Columns 150 x 4.6 mm. Flow rate, 0.5mL/min. Detection, UV 280 nm. Reproduced from Ref. 48, with permission.

Beside the use of MIPs in conventional HPLC, Mi-polymers may also be established in supercritical fluid chromatography, which is characterized by faster equilibration times combined with the use of the environmental friendly C02 as mobile phase. Although preliminary results show relatively broad peaks, chiral separation could be performed based on polymers imprinted with an enantiomer. However, the long-term stability of the photochemically generated polymers seems to be a problem [89]. 

FIGURE 17 Chromatograms of the chiral resolution of Z-tyrosine-OH on Z-(S)-tyrosme-OH-imprinted poly(pentaerythritol triacrylate-co-methylmethacrylate) CSP using chloroform-acetic acid (66 4, v/v) as the mobile phase. (From Ref. 8.)... 

In spite of the development of more successful and reliable CSPs (Chaps. 2-8), these miscellaneous types of CSP have their role in the field of the chiral resolution also. The importance of these CSPs ties in the fact that they are readily available, inexpensive, and economic. Moreover, these CSPs can be used for some specific chiral resolution purpose. For example, the CSP based on the poly(triphenylmethyl methacrylate) polymer can be used for the chiral resolution of the racemic compounds which do not have any functional group. The CSPs based on the synthetic polymers are, generally, inert and, therefore, can be used with a variety of mobile phases. The development of CSPs based on the molecularly imprinted technique has resulted in various successful chiral resolutions. The importance and application of these imprinted CSPs lies in the fact that the chiral resolution can be predicted on these CSPs and, hence, the experimental conditions can be designed easily without greater efforts. Because of the ease of preparation and the inexpensive nature of these CSPs, they may be useful and effective CSPs for chiral resolution. Briefly, the future of these types of CSP, especially synthetic polymers and polymers prepared by the molecularly imprinted technique, is very bright and will increase in importance in the near future. 

Chiral separations by CE and CEC are achieved using a chiral selector which is either free in the mobile phase or immobilised to the stationary phase. MIPs can be used as the selector in both approaches. Molecularly imprinted capillary columns... 

Optical isomer separations that are carried out on a chiral layer produced from C-18 modified silica gel impregnated with a Cu(II) salt and an optically active enantiomerically pure hydroxyproline derivative, on a silica layer impregnated with a chiral selector such as brucine,on molecularly imprinted polymers of alpha-agonists,or on cellulose with mobile phases having added chiral selectors such as cyclodextrins have been reported mostly for amino acids and their derivatives. Mixtures of sorbents have been used to prepare layers with special selectivity properties. 

Ansell, R.J. and Kuah, K.L., Imprinted polymers for chiral resolution of ( )-ephedrine understanding the pre-polymerization equilibrium and the action of different mobile phase modifiers, A a/yif, 130, 179-187, 2005. 

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