LC with electrochemical and UV detection for analysis of a formulation containing gentamicin and parabens

This work describes two separate liquid chromatographic (LC) methods which were developed to control gentamicin sulphate and its preservatives methylparaben and propylparaben in an injectable formulation for veterinary purposes. Owing to the absence of a UV absorbing chromophore in the gentamicin molecule, LC combined with pulsed electrochemical detection (LC-PED) was found to be suitable for the determination of this drug in the formulation. The LC-PED methods from edition 7.0 (valid till 06/2012) and 7.5 (supplement valid from 07/2012) of the European Pharmacopoeia (Ph. Eur.) were compared. The currently recommended LC-PED method allowed good separation between the main gentamicin components and their impurities without interference from additives. Because of its better performance the actual method was used to investigate the degradation profile of the gentamicin sulphate injection. Results obtained from the forced stability study showed that the formulation was stable to oxidative and thermal stress. For the control of the preservatives, a LC-UV method was applied. Both methods were found to be specific, linear and precise. Hence, these two LC methods can be used for routine analysis of the gentamicin sulphate injection.