Ion chromatography method and validation for the determination of sulfate and sulfamate ions in topiramate drug substance and finished product.

A stability-indicating assay method has been developed for monitoring topiramate degradation in drug substance and finished product by quantifying sulfamate and sulfate ions. Topiramate in the solid state is stable under ambient conditions but can degrade under stress conditions (elevated temperatures and humidities). This method detects and quantitates sulfamate and sulfate ions (the inorganic part of the decomposition) and in conjunction with an assay method for topiramate and its known organic degradation product provides total molar accountability. The chromatographic system consists of a sodium hydroxide gradient (2-25 mM) and an anion-exchange HPLC column and an anion suppressor. The analysis is complete in 30 min. The method utilizes the same sample preparation as the topiramate assay method which increases sample efficiency and throughput. The method has been validated for analysis of degraded and nondegraded topiramate drug substance and finished product.