When sourcing Estradiol (CAS No. 50-28-2), it is critical to ensure the product complies with international pharmacopoeia standards such as USP (United States Pharmacopeia), BP (British Pharmacopoeia), or EP (European Pharmacopeia). Suppliers must provide a Certificate of Analysis (COA) for every batch, detailing purity levels (typically ≥98%), melting point, and heavy metal content. Furthermore, prioritize manufacturers with GMP (Good Manufacturing Practice) certification and ISO 9001 to ensure consistent quality control.