FLUORIMETRIC DETERMINATION OF ADRENAL CORTICOSTEROIDS: OBSERVATIONS ON INTERFERING FLUOROGENS IN HUMAN PLASMA

Abstract

SUMMARY Simple fluorimetric methods for the determination of corticosteroids are not sufficiently specific to allow the accurate estimation of low concentrations in plasma. It has been noted previously and is confirmed here, that the measured fluorescence is not proportional to the volume of plasma used, but includes a component which is relatively independent of the plasma volume extracted. This gives rise to a positive intercept on the fluorescence axis when fluorescence intensity is plotted against volume. The suggestion that the determination of plasma corticosteroids can be made specific by subtracting the value of this intercept from the measured fluorescence intensity of the plasma sample has been examined. In the light of experimental data and certain theoretical considerations presented here, this suggestion is rejected. It is concluded that the inaccuracy due to interfering fluorogens can be reduced by taking fluorimeter readings within 5 min. of extraction into the fluorescence reagent, but that even then specificity is not complete.