Imides, enantioseparation

Since one or more of the interactions in these systems might originate from the stationary phase, only a two- or a one-point interaction between the solute and the selector is necessary for mechanisms (2) and (3) to occur [50]. However, some of the CMPAs used in HPLC [37,40,51,52] have also been used as chiral selectors in CE [53-56], which indicates that at least one of the separation mechanisms between the selector and enantiomers is selective complex formation in the mobile phase in these cases, since there is no stationary phase present in CE. A recent example by Yuan et al. [57] is presented in Eigure 17.1. The authors introduced the use of (R)-A,A,A-trimethyl-2-aminobutanol-bis(trifluoromethane-sulfon)imidate as the chiral selector for enantioseparation in HPLC, CE, and GC. This chiral liquid serves simultaneously as a chiral selector and a co-solvent. 

Fig. 2 The chromatograms of enantioseparation using (/ )-MA, iV-trimethyl-2-aminobutanol-bis(trifluoromethanesulfon)imidate CIL 5 as chiral selector, (a) propranolol in HPCE, 10 mmol/L CIL 5 voltage, 16 kV, with anodic detection at 254 nm (b) enantioseparation of 2,2 -diamino-l,r-binaphthalene in HPLC eluent H2O-CH3CN (6 4, v/v) containing 10 mmol/L of chiral selector 5, detection, 254 nm (c) enantioseparation of citronellain GC on 5, split ratio 80 1, FID. Adapted from [76]...

The CIL, (7 )-/V,/V,/V-trimethyl-2-aminobutanol-bis(trifluoromethanesulfon) imide (5), was also found to be a good chiral selector for a variety of compounds in GC (Fig. 2). For instance, this CIL afforded good resolution in the enantioseparation of citronellal (Fig. 2C) [76],... 

It was found that the CIL, (/ )-A/,A/,N-trimethyl-2-aminobutanol-bis (trifluo-romethanesulfonyl)imide (5), was a good chiral selector that can be used in HPLC for enantioseparation of compounds such as alcohol, amine, and amino acids. The presence of this CIL in the mobile phase led to the enantioseparation of 2,2 -diamino-l,r-binaphthalene (Fig. 2B) [76]. Clearly, these limited studies using CILs in HPLC suggest that more CILs with multiple functional groups need to be explored for enantioseparation of various chiral molecules in HPLC. 

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