Determination of erythromycin in gastric juice and blood plasma by liquid chromatography and electrochemical detection.

A liquid chromatographic method for determination of the antibiotic erythromycin in biological samples is described. Erythromycin and the internal standard, oleandomycin, were extracted from alkalinized samples with a mixture of 1-hexane and 2-butanol. After evaporation and reconstitution of the sample, separation was performed on a base-deactivated octadecylsilica column. The effects of pH in the mobile phase and of column temperature on the chromatographic performance were studied. Multiple and irregularly shaped peaks were obtained for some chromatographic systems, but by choosing appropriate conditions erythromycin could be eluted as a single symmetric peak. The absolute recovery was above 90% for erythromycin from blood plasma and above 85% from gastric juice. The limits of quantitation were 20 nM and 100 nM, respectively. Comparison of analytical results for a series of authentic samples with a microbiological assay showed excellent agreement.