A modified sensitive spectrofluorometric method for the determination of propranolol in serum

A modification of the spectrofluorometric propranolol procedure of Shand and associates and Ambler and colleagues is presented. A 3-ml volume of propranolol in serum is made basic with sodium hydroxide and extracted with 1.5% isoamyl alcohol in n-heptane. The drug is back-extracted into a mixture of 0.01 M citric acid in 50% ethylene glycol and measured spectrofluorometrically with the use of 299 nm for excitation and 352 nm for emission. Excellent linearity is observed in the 25--200 ng/ml range. The effects of sodium hydroxide, citric acid, and ethylene glycol concentration on the procedure were investigated. Ethylene glycol--citric acid in water is a better back-extracting mixture from the organic phase than hydrochloric acid. Using pentyl acetate as the extracting solvent instead of isoamyl alcohol in n-heptane did not change significantly the amount of the drug extracted. Other extracting solvents investigated did not increase sensitivity. At high citric acid concentrations a decrease in fluorescence intensity was observed at 350 nm. Interferences from other drugs using this procedure were investigated. Quinidine, methaqualone, and procainamide interfere at therapeutic levels.