Simultaneous determination of metformin in combination with rosiglitazone by reversed-phase liquid chromatography.

A simple, rapid, and precise reversed-phase liquid chromatographic method is developed for the simultaneous determination of metformin in combination with rosiglitazone. This method uses a Zorbax XDB C(18) 15-cm analytical column, a mobile phase of acetonitrile and buffer containing 10mM disodium hydrogen phsosphate, and 5mM sodium dodecyl sulphate in the ratio of 34:66 (v/v), and pH is adjusted to 7.1 with orthophosphoric acid. The instrumental settings are a flow rate of 1 mL/min, column temperature at 40 degrees C, and detector wavelength of 226 nm. The internal standard method is used for the quantitation of metformin and rosiglitazone. Methylparaben is used as an internal standard. The method is validated and shown to be linear. The correlation coefficients for metformin and rosiglitazone are 0.9996 and 0.9997, respectively. The relative standard deviation for six replicate measurements in two sets of each drug in the tablets is always less than 2%.