New spectrophotometric method for the determination of some drugs with iodine and wool fast blue BL

A simple, sensitive and selective method is proposed for the spectrophotometric determination of drugs, viz. ampicillin, penicillin V, amoxycillin, cloxacillin, cefadroxil, ceftezoxime, griseofulvin, streptomycin, nicoumalone and acebutolol HCl, based on their reactivity with iodine. The method involves the addition of excess iodine of known concentration to the drug in the presence of NaOH and the unreacted iodine is determined by the measurement of the decrease in the absorbance of the dye wool fast blue BL (λ_max=540 nm) which was found to be the most suitable of several dyes tested. This method was applied for the determination of drug contents in pharmaceutical formulations and enabled the determination of the drugs in microgram quantities (0.8–9.6 μg ml^?1). No interferences were observed from excipients and the validity of the method was tested against reference methods.