Tramazoline impurity B – mixture of: 1-acetyl-2-[(5,6,7,8-tetrahydronaphthalen-1-yl)amino]-4,5-dihydro-1H-imidazole and N-(4,5-dihydro-1H-imidazol-2-yl)-N-(5,6,7,8-tetrahydronaphthalen-1-yl)acetamide