Methotrexate EP Impurity G Catalogue G101337 CAS 2519848-42-9 M.W 587.60 M.F C28H29N9O6 Specifications FAQs (4-(4-(((2,4-diaminopteridin-6-yl)methyl)(methyl)amino)-N-methylbenzamido)benzoyl)-L-glutamic acid