LIQUID-CHROMATOGRAPHIC ANALYSIS OF A FORMULATION CONTAINING POLYMYXIN, GRAMICIDIN AND NEOMYCIN

The development of a liquid chromatographic assay system for the stabi lity study of a formulation containing polymyxin, gramicidin and neomy cin is described. For the determination of each group of antibiotics, poly(styrene-divinylbenzene) is used as the stationary phase. The mobi le phase for the determination of polymyxin consists of an aqueous sol ution containing 7 g l(-1) of sodium sulfate, 50 ml l(-1) of 1 M phosp horic acid and 160 ml l(-1) of acetonitrile. UV detection is performed at 215 nm. Gramicidin is chromatographed with a mixture of tetrahydro furan-water (38:62) and detected by UV at 222 nm. An aqueous solution containing 70 g l(-1) of sodium sulfate, 1.4 g l(-1) of sodium octanes ulfonate and 50 ml l(-1) of 0.2 M phosphate buffer pH 3.0 is used as t he mobile phase for the determination of neomycin. Since neomycin has no UV-absorbing chromophore, pulsed electrochemical detection is chose n to determine neomycin. For each method, the influence of the differe nt chromatographic parameters on the separation, the selectivity towar ds the other active compounds and the excipients, the repeatability an d the linearity were investigated. The stability of the formulation wa s examined at 0, 6 and 12 months.