Retention times and molecular shapes: the use of desoxycholic acid in column liquids for gas chromatography

Abstract

Desoxycholic acid is known to form inclusion compounds with molecules of restricted width. Retention times have been measured using column liquids containing desoxycholic acid dissolved in either tritolyl phosphate or benzyldiphenyl, and these have been compared with retention times for pure tritolyl phosphate and benzyldiphenyl. The mixed phase containing benzyldiphenyl does not show any appreciable selectivity for n-hydrocarbons relative to their branched homologues, but that containing tritolyl phosphate strongly retards n-hydrocarbons with an unexpectedly large log retention increment per methylene group. Accompanying this large retention, the anomalously retarded peaks are asymmetrical and unusually broad, to the extent that it is impossible to detect the emergence of n-dodecane from this column. The peaks of all other compounds are of more normal width, and their retentions conform to established patterns.