Cyclodextrin-silica columns, displacement

Displacement Chromatographic Separations on / -Cyclodextrin—Silica Columns... 

The Effects of Eluent Temperature. m agreement with previous studies (67), both solute retention and separation selectivity were found to increase significantly as the eluent temperature was reduced from 30 to 0 C, as shown in Fig. 6 for the enantiomers of tryptophan. The change is much larger than what is observed on an octadecylsilica reversed-phase column and the improved separation selectivity is attributed to more pronounced inclusion complex formation. Solute retention decreases precipitously when the temperature of the eluent is raised to or above 60 C, an important fact that can be utilized advantageously for the rapid removed, of strongly adsorbed components (such as displacers) from the cyclodextrin-silica column. 

Aromatic phenols and alcohols were also found to act as good displacers on cyclodextrin-silica columns (67,69). Since the retention studies discussed above indicate that p-nitrophenol is more retained (Fig. 2) than the chloroaniline isomers (Fig. 3), and 4-t-butyl cyclohexanol is more retained than the Ibuprofen enantiomers (Fig. 4), p-nitrophenol and 4-t-butylcyclohexanol were selected as possible displacers for the separations discussed below. 

Displacement chromatogram of a chloroaniline mixture containing 44.7 umol of the meta isomer, 29.8 umol of the ortho isomer and 16.4 umol of the para isgmer. Conditions 50 cm x 4.6 mm ID beta-cyclodextrin-silica column, carrier solvent 10 % v/v methanol water displacer 13 mM p-nitrophenol dissolved in the carrier solvent displacer flow-rate 0.2 mL/min column temperature 30 C. 

Reconstructed displacement chromatogram of a racemic mixture of 0.5 umol Ibuprofen. Conditions as in Fig. 11. Collected fraction size 60 uL. The collected fractions were analyzed on a 25 cm x 4.6 mm ID beta-cyclodextrin-silica column using a 70 % acetonitrile water eluent, which contained 5 mM triethylamine and its pH was adjusted to 6.0 by acetic acid. 

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