A CAS Registry Number is one of the most useful identifiers in chemical documentation. This article explains what it is and how to use it correctly.
What a CAS number is
Assigned by the Chemical Abstracts Service, a CAS number is a unique numeric identifier for a specific substance, written as three hyphen-separated groups of digits. It removes ambiguity that arises from the many names a compound can have (see synonyms & nomenclature).
Different forms, different numbers
A free base and its salt are distinct substances and carry different CAS numbers. Phenibut, for example, has one CAS number for the free base and another for the hydrochloride salt — detailed on our identifiers page. Always document the CAS for the exact form you have.
Using it in records
Record the CAS number with the material name and lot so documentation can be matched unambiguously to the physical sample.
For Research Use Only. Not for human or animal consumption. Nothing here is medical advice, a health claim, or usage guidance. No statement has been evaluated by the U.S. FDA. See our Disclaimer.