Isolation of decomposition products of tylosin using liquid chromatography.

Decomposition products of tylosin A were isolated using open column chromatography and preparative liquid chromatography. Two decomposition products, formed in slightly alkaline medium, were identified as epimers of tylosin A aldol, one of which has been described previously. Another decomposition product was formed on exposure of a tylosin A solution to light. Isomerization of the double bond between C12-C13 takes place, resulting in the formation of the hitherto unreported isotylosin A.

Quantitative analysis of quaternary ammonium antiseptics using thin-layer densitometry.

A thin-layer chromatography method for quantitative analysis of quaternary ammonium antiseptics is described. Silanized silica gel was used as the stationary phase. The mobile phase consisted of methanol-25% (m/v) sodium acetate solution-acetone (65:35:20). The method is able to separate the chain homologues of benzalkonium chloride, cetylpyridinium chloride and cetrimide. Detection was performed using a colour reaction with potassium triiodide solution. The different homologues were quantified using UV densitometry at 400 nm. A number of commercial samples was analysed using this method. From the results it appears that it is worthwhile to have a limit test for the composition of quaternary ammonium antiseptics in pharmacopoeial monographs, the more so as the antibacterial activity depends on it.

Study of the stability of erythromycin in a hydrophilic creme basis by liquid chromatography.

The stability of the macrolide antibiotic erythromycin, incorporated at a 2% m/m concentration in a hydrophilic creme basis containing 2% m/m of chlorocresol, was monitored over a period of 2 months using liquid chromatography as the analytical method. Extracts of the creme were analysed using wide-pore poly(styrene-divinylbenzene) PLRP-S 1000 A as the stationary phase and a mixture of 2-methyl-2-propanol-acetonitrile-potassium phosphate buffer (pH 11.0; 0.02 M)-water (165:30:50:755, v/v/v/v) as the mobile phase. The method showed good selectivity towards chlorocresol, erythromycin A, its related substances and degradation products. As the pH of the creme containing erythromycin was 8.6, alkaline degradation products were expected to be formed. The presence of pseudoerythromycin A enol ether was observed after storage of the creme for 1 week at a temperature of 25 degrees C. After 1 month the content of erythromycin was still more than 95%.

Study of the stability of tylosin A in aqueous solutions.

The decomposition of the 16-membered ring macrolide antibiotic tylosin A in aqueous buffers has been investigated in the pH range 2-13, by means of a liquid chromatographic assay with ultraviolet detection at 280 nm. In acidic medium, tylosin A is converted into tylosin B, while in neutral and alkaline medium, tylosin A aldol is formed together with a number of polar decomposition products of unknown identity. The decomposition kinetics have been studied as a function of the type and concentration of the buffer, ionic strength, pH and temperature.

Analysis of erythromycin estolate by liquid chromatography.

A method is described for the determination of erythromycin estolate by liquid chromatography. A C18 reversed-phase column (25 x 0.46 cm i.d.) was used with acetonitrile-tetrabutylammonium sulphate (pH 6.5, 0.2 M)-phosphate buffer (pH 6.5, 0.2 M)-water [x:5:5:(90-x), v/v/v/v] as mobile phase. The proportion of acetonitrile (x) has to be adapted to the type of stationary phase used. For RSil C18 LL 42.5% (v/v) was used. The column was heated at 35 degrees C, the flow rate was 1.5 ml min-1 and UV detection was performed at 215 nm. The main component, erythromycin A propionate, was separated from all other components which were present in commercial samples. The impurities most frequently observed were the propionate ester of erythromycin C and the amide N-propionyl-N-demethyl-erythromycin A. Erythromycin A was shown to be present in specialties.

Determination of erythromycin ethylsuccinate by liquid chromatography.

A method is described for the determination of erythromycin ethylsuccinate by liquid chromatography. A C18 reversed-phase column (25 cm x 4.6 mm I.D.) was used with acetonitrile-0.2 M tetrabutylammonium sulphate (pH 6.5)-0.2 M phosphate buffer (pH 6.5)-water [x:5:5:(90-x)] as mobile phase. The proportion of acetonitrile (x) has to be adapted to the type of stationary phase used. For RSil C18 LL, 42.5% was used. The column was heated at 35 degrees C, the flow-rate was 1.5 ml/min and UV detection was performed at 215 nm. The main component, erythromycin A ethylsuccinate, was separated from all other components which were present in commercial samples. The main impurities were erythromycin A and the ethylsuccinate esters of erythromycin B and C. The amide N-ethylsuccinyl-N-demethylerythromycin A was shown to be present in all the samples examined. The method was successfully applied to the analysis of specialities.