Diclofenac EP Impurity E, chemically identified as 1,3-Dihydro-2H-indol-2-one (Oxindole) and designated Diclofenac USP Related Compound E, is a bicyclic indolin-2-one process impurity associated with Diclofenac, with molecular formula C₈H₇NO and molecular weight 133.15 g/mol. Unlike Diclofenac EP Impurity A, this compound carries no 2,6-dichlorophenyl substituent and therefore cannot form by degradation of the API itself; it is typically traced to intramolecular cyclization of non-arylated chloroacetanilide-type intermediates or to oxindole-containing starting materials used in certain Diclofenac synthetic routes. Given this origin, the compound serves as a reference marker for process-impurity tracking, starting-material control, and specificity testing in HPLC methods for Diclofenac drug substance and dosage forms. Manufactured at Chemicea under tightly controlled synthetic and analytical protocols, this reference standard supports impurity identification, method validation (AMV), and QC testing in line with EP, BP, and USP requirements, with full applicability to ANDA and DMF regulatory filings. Each batch is supplied with a comprehensive Certificate of Analysis supported by HPLC, ¹H-NMR, and Mass Spectrometry characterization data, ensuring dependable analytical traceability for regulatory and QC laboratories. CAS No. 59-48-3 | Explore complete technical documentation, Safety Data Sheet (SDS), and pricing.