Methotrexate EP Impurity E Catalogue G101335 CAS 19741-14-1;70844-48-3(hemihydrochloride) M.W 325.33 M.F C15H15N7O2 Specifications FAQs 4-[[(2,4-Diaminopteridin-6-yl) methyl] methyl amino]benzoic acid