European Pharmacopoeia (EP) Reference Standard Synonym(s): (2 R ,6 R ,7 R )- and (2 S ,6 R ,7 R )-7-{[(2 R )-2-Amino-2-phenylacetyl]amino}-3-chloro-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-3-ene-2-carboxylic acid Empirical Formula: C15H14ClN3O4S Formula Weight:...