Amoxicillin Impurity C, with CAS number 94659-47-9, is a specified impurity associated with the widely used beta-lactam antibiotic, amoxicillin. It is chemically identified as (2S,5R,6R)-6-[[(2R)-2-amino-2-(4-hydroxyphenyl)acetyl]amino]-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]heptane-2-carboxylic acid, which is the amoxicillin molecule itself. This designation arises because it is a key reference standard for the main active pharmaceutical ingredient (API) during quality control. Its primary and critical application is in the pharmaceutical industry for analytical purposes. It serves as a certified reference material (CRM) or impurity standard used in high-performance liquid chromatography (HPLC) and other analytical techniques. Its use is essential for the identification, quantification, and control of amoxicillin content and related substances in drug substances and finished pharmaceutical products, ensuring compliance with pharmacopoeial standards (e.g., USP, EP) and regulatory requirements for safety and efficacy. As a pharmacopeial reference standard, it is not used therapeutically but is vital for maintaining the quality and purity of commercial amoxicillin preparations. Proper handling requires standard laboratory safety precautions.