Erythromycin is a common antibiotic used for the treatment of bacterial infections. Standard erythromycin contains four related compounds, erythromycin A, B, C and D. Each of them has different antibacterial activity, where erythromycin A is the most active.

During the Karl Fischer titration of different erythromycin samples we found out that they can behave differently. Erythromycin A undergoes a pH-dependant side reaction causing unstable endpoints, so the working medium needs additional buffering. In a sample declared as Erythromycin only, the end points have been much more stable and standard reagents can be used. Both one-component and two-component volumetric titration is recommended.

Hydranal-Water Standard 10.0, Hydranal-Water Standard 1.0, and Hydranal-Standard Sodium Tartrate Dihydrate are suitable for determination of the titer or control of the volumetric determination.