MEASUREMENT OF URINARY FREE CORTISOL BY STABLE-ISOTOPE DILUTION MASS-SPECTROMETRY USING A NEW CORTISOL DERIVATIVE

The reaction of the bismethylenedioxy derivative of cortisol (cortisol -BMD) with heptafluorobutyric anhydride to give the corresponding 3,5- dienol heptafluorobutyrate (cortisol-BMD-HFB) has been shown to procee d with dehydration. Acid-promoted dehydration of either cortisol-BMD o r cortisol-BMD-HFB, or concurrent dehydration of bath, is the proposed reaction mechanism leading to a trienol heptafluorobutyrate, whose ch romatographic properties and mass spectral data are consistent with th e additional double bond in the C-9-C-11 position. Forming the 3,5-die nol heptafluorobutyrate of cortisol-BMD in benzene rather than acetone gave a compound whose chromatographic properties and mass spectral da ta were different to that of the 3,5,9(11)-trienol heptafluorobutyrate but consistent with that of a cortisol-BMD-HFB. The mass fragmentomet ry of this new cortisol derivative was found to be more suited to the technique of isotope dilution mass spectrometry than the 3,5,9(11)-tri enol heptafluorobutyrate, and thus was applied to our intended goal of measuring urinary free cortisol by gas chromatography-mass spectromet ry, An efficient and convenient solid-phase extraction technique is em ployed in our assay to isolate cortisol from 5 ml of urine.