Diazepam EP Impurity C, chemically defined as 3-Amino-6-chloro-1-methyl-4-phenylquinolin-2(1H)-one and designated Diazepam USP Related Compound B, is a quinolinone (carbostyril)-type related substance of Diazepam, with molecular formula C₁₆H₁₃ClN₂O and molecular weight 284.74 g/mol. Structurally, this impurity corresponds to a ring contraction of the seven-membered 1,4-benzodiazepine nucleus into a six-membered 3-aminoquinolin-2(1H)-one scaffold, and it can arise both as a process-related impurity and as a transformation product of the parent anxiolytic API under stress conditions. As a specified impurity in the pharmacopoeial monographs, the compound serves as an important reference marker for impurity profiling, stability-indicating method development, and forced-degradation studies across Diazepam drug substance and formulation batches. Manufactured at Chemicea under strictly controlled synthetic and purification protocols, this reference standard supports impurity identification, analytical method validation (AMV), and quality-control testing in line with the EP and USP monographs for Diazepam. 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 submissions and ANDA filings. CAS No. 5220-02-0 | Explore complete technical documentation, Safety Data Sheet (SDS), and pricing.