4-[2-hydroxy-3-(propan-2-ylamino)propoxy]benzoic acid; 4-(2-Hydroxy-3-isopropylaminopropoxy)benzoic Acid; 4-[2-Hydroxy-3-[(1-methylethyl)amino]propoxy]benzoic Acid; Bisoprolol Acid Impurity; Bisoprolol Impurity 13