Ly. Tang et al., A comparative study of factors affecting chiral separations under reversed-phase conditions using cellulosic and Pirkle-type chiral selectors, ENANTIOMER, 5(3-4), 2000, pp. 345-355
Limited studies have been conducted in reversed-phase chiral chromatography
despite the relevance to water soluble chiral analytes. Systematic investi
gation and interpretation of factors affecting chiral separation in reverse
d-phase LC is crucial to efficient chiral method development. Two of the mo
st useful chiral stationary phases (CSPs), a cellulosic (Chiralcel OJ-R) an
d a Pirkle-type (Chirex 3005), were chosen as the chiral selectors in this
study to systematically investigate the factors affecting chiral separation
of a series of Fmoc-amino acids. The effects of temperature, pH, buffer co
ncentration, buffer type and organic modifiers on retention and chiral sele
ctivity were compared between the cellulosic and the Pirkle-type selectors.
Temperature affected retention and selectivity, as predicted by thermodyna
mics, using both types of chiral selectors. On the cellulosic CSP, buffer p
H was the only factor which caused a significant change in chiral selectivi
ty, while several factors, including buffer concentration and organic modif
ier type, affected chiral selectivity on the Pirkle-type CSP. The results a
lso indicated that the cellulosic CSP had a retention mechanism analogous t
o conventional reversed-phase LC, however, the Pirkle-type selector appeare
d to show a mixed mode retention mechanism for these analytes.