THE DETERMINATION OF ADRENOCORTICAL STEROIDS IN BLOOD: OBSERVATIONS ON THE RELIABILITY OF A SIMPLE FLUORIMETRIC METHOD FOR CORTISOL

Abstract

SUMMARY A simple method for the determination of cortisol in human plasma has been improved and studied in detail. The specificity for cortisol was increased by an additional partition of the extract between benzene and water. This did not obviate the use of a preliminary petrol partition to remove some material interfering with the determination. Quenching or potentiation of fluorescence by impurities is common, and an 'internal standard' technique, consisting of addition of cortisol to parallel plasma samples, was adopted in an attempt to improve the accuracy of the method. Careful cleaning of all glassware is essential for satisfactory accuracy. A preliminary estimate of precision indicates that plasma cortisol concentrations of 2 μg./100 ml. are distinguishable from zero, but satisfactory precision (error ≤ 15%, P = 0·05), at concentrations of 10 μg./100 ml. or greater, still requires samples of 8 ml. of plasma.