Foscarnet Sodium EP Impurity B;FOSCARNET IMPURITY B;1-Ethoxy-1-hydroxyphosphinecarboxylic acid 1-oxide disodium salt;Disodium (ethoxyoxydophosphanyl)formate;Foscarnet sodium hexahydrate EP Impurity B;Benzenemethanol,3-bromo-7-ethyl-;Foscarnet Related Compound B as Disodium Salt;Foscarnet Sodium Hexahydrate Impurity B as Disodium Salt