Development of a urinary free cortisol assay using solid-phase extraction-capillary electrophoresis

In clinical practice, the measurement of urinary free cortisol (UFC) provid es the most sensitive and specific diagnostic information for excess adrena l production of cortisol. The existing methodologies (RIA and HPLC) are tim e consuming, costly, involve tedious extractions, derivatizations and probl ems with non-specific interactions with cortisol metabolites in urine. In t he present study, we describe the development of an SPE-CE method for the r apid analysis of UFC. UFC was concentrated using SPE C-18 cartridges (3M Em pore) under a vacuum and eluted with acetonitrile-SDS. The use of 10% aceto ne to wash cartridges before final elution with acetonitrile-SDS showed sig nificant improvements in the free cortisol recovery. The complete extractio n was accomplished in 10-15 min with a recovery of 89-94%. CE analysis was done on a Beekman P/ACE 5010 with detection at 254 nm using a neutral capil lary. Detection limits of free cortisol in urine was improved to 10 mu g/l with SPE compared to 500 mu g/l without SPE. No interferences either from B SA or other urinary cortisol metabolites affected the free cortisol determi nations. The results showed the feasibility of a rapid UFC detection with i mproved sample handling capacity. (C) 1999 Published by Elsevier Science B. V. All rights reserved.