Colorimetric prednisolone assay and its application to dissolution studies

The colorimetric method of Porter and Silber, originally developed for assaying cortisone and related corticosteroids, was adapted to the assay of prednisolone in the presence and absence of a surfactant, octoxynol 9. Optimal conditions for the colorimetric reaction between prednisolone and acidified phenylhydrazine solution were 30 min at 50 degrees C. The slight interference of octoxynol 9 with the absorbance of the yellow prednisolone-phenylhydrazine complex at 410 nm was corrected by adding an equal surfactant concentration to the blank. When freshly prepared acidified phenylhydrazine solutions were used, the colorimetric method had a sensitivity of 0.2 microgram/mL and a precision of 0.1 microgram/mL. Its averaged relative standard deviation was 3.7% in the prednisolone concentration range of 10-300 micrograms/mL.