A CAS number is a globally recognized, unique numerical identifier assigned to a specific chemical substance. This standardized system ensures a substance can be precisely identified, regardless of the language, region, or nomenclature used to describe it. It serves as a universal fingerprint for chemicals, allowing for clear communication across scientific, industrial, and regulatory sectors worldwide. The number is maintained in an extensive database, establishing a common language for identifying millions of known chemical compounds.
What the CAS Registry Number Represents
CAS is an acronym that stands for Chemical Abstracts Service, which is a division of the American Chemical Society (ACS). This organization is responsible for assigning and maintaining the CAS Registry Number, often abbreviated as CASRN. The numbers are recorded in the CAS Registry, a comprehensive database that tracks and indexes every chemical substance described in the scientific literature.
The CAS Registry was established in 1965 to address the growing problem of inconsistent and confusing chemical nomenclature. It provides an authoritative collection of information on organic and inorganic substances, alloys, polymers, and minerals. When a new substance is identified, CAS scientists analyze it and assign a new, unique number in sequential order. This ensures the number itself does not contain inherent chemical information about the substance’s structure or properties.
Anatomy of a CAS Registry Number
A CAS Registry Number is composed of up to 10 digits, which are separated into three distinct parts by hyphens. The structure is formatted as a sequence of numbers, followed by a hyphen, then two more numbers, and finally a hyphen and a single digit (e.g., XXXXXX-XX-X). The first part of the number can have anywhere from two to seven digits and acts as the unique serial identifier. The middle section is always composed of two digits.
The final segment is a single number known as the check digit. This digit is calculated using a specific mathematical algorithm based on the preceding digits in the number. The check digit’s purpose is to provide a simple mechanism for verifying the number’s validity and accuracy, effectively catching transcription or input errors. By performing the calculation, a user can quickly confirm whether a number is genuine.
Why Unique Identification is Crucial
The CAS number system resolves the inherent confusion caused by chemical substances often having multiple, conflicting names. A single compound might be known by its systematic IUPAC name, a common name, various trade names, or regional synonyms, leading to potential errors in communication. For example, a substance and its different isomers—molecules with the same chemical formula but different structural arrangements—will each have a distinct CAS number, preventing dangerous mix-ups.
This standardized identification is important in safety and regulatory compliance worldwide. Governmental agencies and international organizations rely on the CAS number to monitor and track chemicals for environmental and health purposes. The number is a mandatory component on Safety Data Sheets (SDS), ensuring that workers and emergency responders can instantly access accurate hazard, handling, and storage information. In international trade, the unambiguous nature of the CAS number facilitates smooth transactions and compliance across borders.