Sample-pretreatment procedure for routine liquid chromatographic assay of serum cortisol

A specific method for measuring concentrations of cortisol in serum, by preliminary isolation on a "minicolumn" followed by elution and determination by liquid chromatography, is described. This assay requires only 500 microl of serum. The limit of determination of cortisol was found to be 5 microg l . The analytical recovery of cortisol added to serum ranged from 98 to 102%. The coefficients of variation ranged from 2.4 to 3.4% (within-day) and from 3.6 to 8.8% (day-to-day), depending on the cortisol concentration. The method compares well with a commonly used radioimmunological method.