Improved automatic kinetic method for the determination of various corticosteroids.

Two reaction-rate methods for the determination of corticosteroids at the micromolar level were developed. The methods are modifications of the widely used Blue Tetrazolium and Porter-Silber reactions which are employed for the automatic kinetic determination of corticosteroids using the continuous-addition-of-reagent (CAR) technique. The CAR technique avoided all technical problems typically associated with these reactions such as long incubation at high temperatures, high blank values, and turbidity. On the basis of its analytical figures of merit, the Blue Tetrazolium method was chosen; it allows corticosteroids to be determined at concentrations from 2.7 x 10(-6) to 1.9 x 10(-4) M at a rate of 25 samples/h (triplicate analyses) with an root mean square deviation of ca. 3%. The proposed method was evaluated in recovery experiments and analyses of commercially available formulations.