CAS Registry Number

CAS Registry Number is a unique numerical identifier assigned to every chemical substance described in the open scientific literature (including organic and inorganic compounds, minerals, isotopes, alloys, and mixtures). It is used to provide a standardized method of identifying chemical substances. The Chemical Abstracts Service (CAS), a division of the American Chemical Society, assigns these identifiers as part of its "CAS REGISTRY" database. This database is recognized globally as the most authoritative source for chemical information.

Overview

The CAS Registry Number itself has no chemical significance but is simply a way to identify a substance without the ambiguity of chemical nomenclature. Numbers are assigned in a sequential order and, as of 2023, there are over 150 million substances registered. The CAS Registry Number is used internationally by researchers, regulatory agencies, and industries to access and share chemical information, including physical and chemical properties, safety data, and regulatory information.

Format

A CAS Registry Number is typically a series of digits divided by hyphens into three parts. The rightmost segment consists of a single check digit, the middle segment consists of two or three digits, and the leftmost segment (which can be as long as seven digits) increases sequentially as new numbers are assigned. For example, the CAS Registry Number for water is 7732-18-5.

Applications

CAS Registry Numbers are used extensively in chemistry, biology, and related disciplines. They serve as a reliable means of identifying specific chemicals in databases, research papers, regulatory documents, and safety datasheets. This simplification helps avoid confusion that might arise from the use of common or similar names for different substances or the same name for different substances.

Obtaining a CAS Registry Number

New substances can be assigned a CAS Registry Number when they are reported in the scientific literature or introduced into commerce. The process involves the submission of a chemical structure or a detailed description to CAS, where it is analyzed and, if accepted, added to the CAS REGISTRY database with a newly assigned number.

Limitations

While the CAS Registry Number is a powerful tool for identifying chemical substances, it does not convey any chemical, physical, or biological information about the substance itself. Additionally, the proprietary nature of the CAS REGISTRY database means that access to the full range of information associated with a CAS Registry Number can require a subscription.

See Also

• Chemical Abstracts Service
• International Chemical Identifier (InChI)
• Simplified Molecular Input Line Entry System (SMILES)
• Chemical nomenclature
• Chemical database