Modified colorimetric method of plasma prednisolone.

A simple, precise, rapid, and sensitive colorimetric method was adapted for the quantitative analysis of prednisolone in dog plasma. A paper chromatographic procedure was modified by the use of thin-layer plates coated with microcrystalline cellulose. Heparinized blood samples were separated from the cellular elements and extracted with methylene chloride. After washing with acid and alkali, the extract was evaporated to dryness. The residue was dissolved in methanol and streaked on the TLC plate. After development, the band that was detected by UV light was scraped off and extracted with methanol. The methanol extract was treated with the Porter-Silber reagent (phenylhydrazine). Absorbance was measured at 410 nm. Replicate assays indicated a mean recovery of 97.5% and a coefficient of variation of 5.13%.