Electrochemical studies and differential pulse polarographic analysis of lansoprazole in pharmaceuticals

The electrochemical reduction of lansoprazole was investigated by cyclic vo ltammetry and direct current and differential pulse polarography. The reduc tion potential was -1.32 V vs. Ag/AgCl with a dropping mercury electrode in a supporting electrolyte consisting of phosphate buffer (pH 9.0)-tetrameth ylammonium iodide (4 + 1). The reversibility of the electrode reaction and the type of limiting current were studied. The temperature coefficient and the diffusion constant were determined. A mechanism for the electrode react ion was proposed. A new simple and sensitive differential pulse polarograph ic method was also developed for the quantification of lansoprazole. A line ar calibration graph was obtained in the range 0.04-11.35 mug ml(-1). The l imit of detection was 0.03 mug ml(-1) and the intra- and inter-day precisio ns were 0.84-2.32 and 0.72-3.09%, respectively. The developed method was ap plied to six different commercial pharmaceutical capsule preparations conta ining enteric-coated granules. The relative standard deviations ranged from 1.36 to 2.85%. Recovery studies for the accuracy of the method were perfor med by adding a synthetic mixture to known amounts of lansoprazole and the mean recovery was 100.45%. The data obtained from commercial preparations w ere compared with those from a published spectrophotometric method. No diff erence was found statistically.