7 beta,12 beta-Dihydroxy-5 beta-cholan-24-oic acid as an internal standard for quantitative determination of bile acids by gas chromatography.

In order to find an artificial internal standard compound for quantitative determination of bile acids by gas chromatography, 7 alpha,12 alpha-, 7 alpha, 12 beta-, 7 beta, 12 alpha- and 7 beta,12 beta-dihydroxy-5 beta-cholan-24-oic acids were chemically synthesized with cholic acid (1) as the first starting material. The gas chromatographic retention time of 7 beta,12 beta-dihydroxy-5 beta-cholan-24-oic acid (beta beta-isomer) was more different from that of natural bile acids than the other isomers. Moreover, beta beta-isomer was extracted in the same fraction as the bile acids from urine, and no urinary substance had the same retention time as beta beta-isomer. No artifact was produced from beta beta-isomer during the analysis procedure. It was concluded that the beta beta-isomer is an internal standard compound with certain advantages for the quantitative determination of bile acids in urine by gas chromatography, irrespective of the recovery rate during the analysis procedure.