Abstract
“Polarities” of commercial modified cyclodextrin (CD) gas chromatographic phases were rated at 100 °C by the averages of retention indices for eight McReynolds' probe solutes, by the sequence and proportion of three, and by values for two of them. All nine CDs studied are above the low polarity of a fully methyl polysiloxane, and below the high values of a polyethylene glycol. Values from some CDs are similar to those of polar substituted polysiloxanes. Modifications of α-CD are of lower polarity than their corresponding larger CDs. Dipentyl-(hydroxy remaining)-CDs are of lowest polarity and hydroxypropyl-dimethyl-CDs the highest. Esterified-(dipentyl)-γ-CDs fall between these groups, along with a supposedly fully methyl-β-CD. Surprisingly, the butyryl ester seems to be more polar than the shorter chain propionyl one. These features can be seen from a triangular plot of retention index fractions of the sum of three McReynolds' probes. The c ratios at higher temperatures, involving two different probe solutes, only seem comparable for different modifications of the same ring size CD.
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