CAS (CAS Registry Number)
At a glance: A unique numeric identifier assigned to one specific chemical substance.
A CAS Registry Number is a unique and unambiguous identifier assigned to a specific substance in the CAS Registry. 22 CAS Registry Numbers are generally serial numbers with a check digit, so they do not encode structural information as SMILES and InChI strings do. 23 Each CAS Registry Number designates only one substance—two substances do not share the same number—so agencies rely on them for regulatory identification. 24