Labetalol EP impurity C;Labetalol Hydrochloride Impurity 3 (Labetalol Hydrochloride EP Impurity C);Labetalol Impurity 13;Benzamide, 2-hydroxy-5-[1-hydroxy-2-[(phenylmethyl)amino]ethyl]-;Labetalol Hydrochloride EP Impurity C;Labetalol EP Impurity C HCl