CAS number

A CAS Registry Number, also known as a CAS Number, is a unique numerical identifier assigned to every chemical substance described in the open scientific literature. It is a service provided by the Chemical Abstracts Service (CAS), a division of the American Chemical Society.

Structure and Format

A CAS Number is a numeric designation that can contain up to 10 digits, divided into three parts by hyphens. The format is as follows:

• The first part can have up to 7 digits.
• The second part has 2 digits.
• The third part is a single check digit.

For example, the CAS Number for water is 7732-18-5.

Purpose and Use

CAS Numbers are used to provide a unique, unmistakable identifier for chemical substances. This is particularly useful in scientific research and industry, where precise identification of substances is crucial. CAS Numbers are used in:

• Chemical databases
• Regulatory compliance
• Chemical inventory management
• Safety data sheets

Assignment Process

CAS Numbers are assigned by the Chemical Abstracts Service when a substance is indexed in the CAS Registry. The assignment is based on the substance's molecular structure and composition, ensuring that each CAS Number is unique to a specific chemical.

Advantages

• Uniqueness: Each CAS Number is unique to its substance, reducing confusion in chemical identification.
• Global Recognition: CAS Numbers are recognized internationally, facilitating global communication and trade.
• Comprehensive Database: The CAS Registry is one of the most comprehensive databases of chemical substances, with millions of entries.

Limitations

• Not Descriptive: CAS Numbers do not provide information about the chemical structure or properties of a substance.
• Proprietary: Access to the full CAS Registry requires a subscription, which can be a limitation for some users.

Also see

• Chemical Abstracts Service
• International Chemical Identifier
• PubChem
• SMILES (Simplified Molecular Input Line Entry System)