Abstract
A gas‐chromatographic separation of underivatized steroids is described, in which the liquid crystal N,Ń‐bis(p‐phenylbenzylidene)α,α′‐bi‐p‐toluidine (BPhBT) was used isothermally at 265°C for the stationary phase. The nematic range of this crystal is 247 to 403°C. Use of the BPhBT crystal allowed operations in a temperature range where steroids are volatile and unlikely to display broad elution peaks and long retention times.
With columns precoated with 2.5 weight percent of BPhBT, steroids containing minor structural differences in the ring system were readily differentiated. For example, 5‐androsten‐17α‐ethinyl‐3β, 17β‐diol was found to elute more rapidly than its 3‐keto analog, ethisterone. Ethisterone was distinguished readily also from its 19‐nor analog, norethisterone. Additionally, differences in side‐chain functionality and resultant molecular dimensions facilitated the separation of steroids of identical ring structure, as in the comparison of cholesterol with methyl 3β‐hydroxy‐5‐cholenate and 25‐hydroxycholesterol.
An enhancement of separation according to the molecular length‐to‐breadth ratio was observed; in general, the larger this length‐to‐breadth ratio, the greater the retention period on the column.