Study of enantioselectivity on an immobilized amylose carbamate stationary phase under subcritical fluid chromatography

Abstract

In this paper, we describe the enantiomeric separation of a chiral alcohol under subcritical fluid chromatography conditions using a 3 μm particle size bonded amylose carbamate stationary phase. Linear and branched alcohols were used as polar modifiers in CO2. The studies with linear alcohols showed a decrease in selectivity factor as the number of carbons in the linear chain increased. For branched alcohols, as the bulk of substituents at the α carbon atom increases the separation factor decreases. Thermodynamic studies showed that in the presence of the alcohols studies, except methanol and ethanol, a positive ΔΔS was observed. Molecular mechanics simulation brought more insights into the mechanism of enantiomeric separation on this stationary phase under subcritical fluid chromatography.

Elucidation of the absolute configuration of rhizopine by chiral supercritical fluid chromatography and vibrational circular dichroism

“…Note that this resolution is only achieved for the acyl derivative on the chiral selector amylose tris(3,5‐dimethylphenylcarbamate). No chiral separation was obtained for the underivatized racemate analyzed on the same column or on a cellulose based stationary phase . The mass spectral data for peak 1 and peak 2 are shown in Fig.…”

Chromatographic behavior of small organic compounds in low‐temperature high‐performance liquid chromatography using liquid carbon dioxide as the mobile phase

“…Recently, the chromatography using mixtures of liquid or subcritical CO 2 and polar modifier (methanol, ethanol, and etc.) at approximately 0–35°C have been attracted . A few separations at low temperatures (>–47.5°C) with CO 2 mobile phases were reported for the separation of enantiomers .…”

Thermodynamic enantioseparation behavior of phenylthiohydantoin‐amino acid derivatives in supercritical fluid chromatography on polysaccharide chiral stationary phases

“…Besides, the stationary phase may undergo a change of conformation as it would be less “swelled” by the solvent, affecting the phenylcarbamate side‐chain mobility . In a swelled stationary phase (thus at lower temperatures), the chiral cavities are expected to be more open to accommodate bulky analytes . (ii) In the second case, when increasing temperature the retention first decreased slowly, reached a minimum at around 20°C then increased sharply, as can be seen in Figure for PTH‐α‐Aminobutyric acid. This case occurred for PTH‐Alanine (example chromatograms are given in Supporting Information Figure S1), PTH‐α‐Aminobutyric acid, PTH‐Aspartic acid, and PTH‐Tyrosine.…”

“…Besides, the stationary phase may undergo a change of conformation as it would be less “swelled” by the solvent, affecting the phenylcarbamate side‐chain mobility . In a swelled stationary phase (thus at lower temperatures), the chiral cavities are expected to be more open to accommodate bulky analytes .…”