Vardenafil EP Impurity B Catalogue F341502 CAS 437717-43-6 M.W 392.43 M.F C17H20N4O5S Specifications FAQs 4-ethoxy-3-(5-methyl-4-oxo-7-propyl-3,4-dihydroimidazo[5,1-f][1,2,4]triazin-2-yl)benzenesulfonic ac