Brush enantioseparation

Brush or Pirkle-type CSPs show promise in the enantioseparation of many classes of compounds, and also have shown to exhibit the high efficiencies expected in CEC separations. The high efficiency of enantioseparations of these CSPs is thought to be due to more favorable mass transfer kinetics between the analytes and these CSPs. Cavender et al. [144] used these CSPs bonded to silica particles to separate 10 chirally active compounds. They used (S)-Naproxen-derived CSP as well as the more widely used (3R, 4S)-Whelk-0. They found that while the (S)-Naproxen-derived CSP gave rise to more reproducible EOF, (3R,4S)-Whelk-0 gave more efficient separations. The reproducibility of the... 

Among brush-type CSPs for HPLC, the Whelk-0(R) CSP, first designed for naproxen enantioseparation, has shown an outstanding applicability for a broad diversity of racemic compounds [72]. Nowadays it has become one of the CSPs of reference included in most screening processes addressed to the search of adequate conditions for enantioselective separation in drug discovery [73, 74]. A CS containing the Whelk-0( skeleton, and a lipophilic chain aimed to enhance solubility... 

The addition of organic acids or bases, for acidic and basic analytes, respectively, at a low concentration (usually 0.1-0.2% v/v) is a common practice in enantioseparation, even when normal phase conditions are used. The most conventionally used additives for this purpose are acetic or tri-fluoroacetic acids and diethyl- or triethylamine as bases, although ethanolamine and ethylenediamine are also frequently used (Figure 54.12). The role of these additives is to prevent ionization of ionizable analytes. When CSPs containing nonionizable CSs, such as polysaccharide derivatives or brush-type CSs, are used, the result is an improved interaction between neutral CSs and enantiomers and an increased efficiency (thinner peaks). 

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