An unknown impurity in lansoprazole (2-[[[3-methyl-4-(2, 2, 2-trifluoroethoxy)-2-pyridyl] methyl] sulfinyl] benzimidazole) was detected by HPLC and was identified as des-(trifluoroethoxy) lansoprazole, an principal synthetic route indicative impurity of lansoprazole. Lansoprazole was subjected to different ICH prescribed stress conditions like hydrolysis, oxidation, photolysis and thermal degradation conditions to enrich the impurity. The impurity was enriched by using acid catalytic degradation, isolated by using preparative HPLC and characterized (FTIR, MS and NMR). Limit of Detection (LOD) and Limit of Quantification (LOQ) are found to be 0.014% and 0.035% respectively.