TLC SEPARATION AND IDENTIFICATION OF NEOMYCIN SULFATE, POLYMYXIN B SULFATE, AND BACITRACIN ZINC IN OINTMENTS

Abstract

The development of a thin-layer chromatography method for the separation and identification of polymyxin B sulfate, neomycin sulfate, and bacitracin zinc in ointments, either alone or in combinations, is described. The ointments were dispersed in chloroform and the components of interest were extracted into an aqueous 0.1 N hydrochloric acid layer. The stationary phase was silica gel G and the mobile phase consisted of a mixture of methanol, ethanol, methylene chloride, ammonium hydroxide, and water (3 : 3 : 2 : 2 : 1.5, v/v) or methanol, isopropanol, methylene chloride, ammonium hydroxide, and water (4 : 2 : 2 : 2 : 1.5, v/v). Detection was performed by spraying with a 0.2% solution of ninhydrin in 1-butanol. A number of commercial samples were analyzed using the described method. Our method worked on all brands tested, except one brand of the three-component ointment (Brand A), which contained interfering excipients. A sample clean-up step was developed to remove the interferences. The method described was compared to the official methods described in the United States Pharmacopeia-National Formulary (USP24-NF19). Our method offered much better separation and well-defined spots compared to the official methods.

ACKNOWLEDGMENT

An article entitled, “Simultaneous identification and quantitative determination of neomycin sulfate, polymyxin B sulfate, zinc bacitracin, and methyl and propyl hydroxybenzoates in ophthalmic ointment by TLC,” by J. Krzek et al. appeared in the J. Pharm. Biomed. Anal., 24, 629–636 while this manuscript was in preparation.