8-Methoxy-1,3-dimethyl-12-thioxopyrido[1',2':3,4]imidazo[1,2-a]benzimidazol-2(12H)-one; Omeprazole specified impurity F [EP]; Omeprazole related compound F [USP]; Omeprazole related compound F; Esomeprazole Impurity 8; Omeprazole Impurity F; Omeprazole EP Impurity F