Validated liquid chromatography method for assay of tizanidine in drug substance and formulated products

A new isocratic stability indicating HPLC method for determination of tizanidine in drug substance and formulated products is described. Chromatographic separation of tizanidine from the related substances and degraded products was achieved with a Hypersil CN column ( mm, 5 μm) using a mobile phase comprising a mixture of an ion-pairing solution of heptanesulphonic acid sodium salt (HAS), methanol and acetonitrile (50:57:18 (v/v)) within 10 min. The flow-rate was 1.0 ml/min and detection was made at 227 nm. The method has good selectivity towards tizanidine, related substances and degraded products. Limits of quantitation for tizanidine and its synthetic intermediates were determined, ranging from 0.051 to 0.54 μg/ml. The linearity range was found to be 2-20 μg/ml (r=0.9998, n=5). Mean recovery for tizanidine from the tablets was from 99.5 to 99.8%. Precision of the method was 1.0% (n=9). The method can be used for routine analysis and the quality control of tizanidine drug substance and its formulated products.