Determination of a ternary mixture of penicillin-G sodium salt, penicillin-G procain salt and dihydrostreptomycin sulphate, by third-derivative spectrophotometry

Abstract

Ternary mixtures of antibiotics, i.e. penicillin-G sodium salt, penicillin-G procain salt and dihydrostreptomycin sulphate salt, are assayed by ‘zero-crossing’ third-derivative spectrophotometry. Calibration plots follows Beer's law up to 40 μg/ml of penicillin-G sodium at 222.5 nm ( r = 0.9997), 46 μg/ml of penicillin-G procain at 217 nm ( r = 0.9999) and 36 μg/ml of dihydrostreptomycin sulphate at 211.5 nm ( r = 0.9999), in the presence of one another. Detection limits at p = 0.05 level of significance were calculated to be, respectively, 0.66, 0.41 and 0.25 μg/ml. The procedure is rapid, simple, nondestructive and does not require solution of equations. The method was successfully applied for determining laboratory mixtures and commercial injections.