How Are CAS Numbers Made

1. How Are CAS Numbers Made? A Beginner’s Guide to Chemical Abstracts Service CAS numbers (Chemical Abstracts Service numbers) are unique numerical identifiers assigned to every chemical substance described in open scientific literature. These identifiers are issued by the Chemical Abstracts Service (CAS), a division of the American Chemical Society (ACS). The CAS number creation process is based on several principles designed to ensure that each substance receives a unique, permanent number that facilitates precise identification. Here’s how they’re made and assigned: 1. 1. Submission and Data Review Submission and Data Review  When a new chemical is discovered or synthesized, its details (structure, composition, properties) are submitted to CAS by researchers, manufacturers, or other scientific entities. CAS scientists and data analysts review the substance to confirm that it is indeed unique and distinguishable from other registered chemicals.  2. 2. Verification of Chemical Structure Verification of Chemical Structure  CAS carefully analyzes the molecular structure to ensure it doesn't duplicate any existing entry. This involves comparing it with the vast library of existing CAS numbers to avoid overlap. The CAS system includes exact structural information, so isomers (chemicals with the same formula but different structures) will receive distinct CAS numbers.  3. 3. Assignment of a Unique Identifier Assignment of a Unique Identifier   Once confirmed as unique, the substance is assigned a CAS number. The CAS number itself is a sequential identifier and does not encode any structural, chemical, or functional information. It simply serves as a unique label to prevent ambiguity and errors. 4. 4. Structure of CAS Numbers Structure of CAS Numbers  CAS numbers are structured in three parts separated by hyphens: xxxxxx-yy-z. o o o The first part (up to six digits) is a unique sequence number. The second part (two digits) is a grouping for additional distinction. The third part (single digit) is a check digit calculated using a specific algorithm to verify the validity of the number, minimizing errors in databases. 5. 5. Database Entry and Availability Database Entry and Availability  After the CAS number is assigned, the information is added to the CAS Registry, one of the largest and most comprehensive databases of chemical substances. This registry is accessible through subscription databases like SciFinder, where researchers and industry professionals can look up substances by their CAS numbers and find details on properties, applications, and associated research. 

2. 6. 6. Updates and Revisions Updates and Revisions  Although each substance has a permanent CAS number, in rare cases, additional registry entries may be created if a chemical's classification or understanding changes significantly. However, CAS numbers are usually stable and remain with the substance for its lifetime in scientific literature. Why CAS Numbers Are So Useful: Why CAS Numbers Are So Useful:  Universality: CAS numbers provide a universal identifier that can be used across different languages, naming conventions, and scientific disciplines. Database Cross-Referencing: CAS numbers are widely integrated into scientific, regulatory, and industrial databases worldwide, making them essential for cross-referencing chemicals.  Overall, CAS numbers are carefully curated and validated, ensuring that each identifier is unique and reliable.