Acitretin - Impurity B(EP) ; Ethyl (all-E)-9-(4-Methoxy-2,3,6-trimethylphenyl)-3,7-dimethylnona-2,4,6,8-tetraenoate ; Etretinate; (all-E)-9-(4-Methoxy-2,3,6-trimethylphenyl)-3,7-dimethyl-2,4,6,8-nonatetraenoic Acid Ethyl Ester; (2E,4E,6E,8E)-Ethyl 9-(4-methoxy-2,3,6-trimethylphenyl)-3,7-dimethylnona-2,4,6,8-tetraenoate; Acitretin Related Compound B (USP);