Why is the CAS number important?

A CAS number, or a Chemical Abstracts Service number, is a unique identifier assigned to every chemical substance that has been described in the scientific literature. CAS numbers are widely used by researchers, regulators, manufacturers, and suppliers to communicate and access information about chemicals accurately and efficiently. In this article, we will explore the history, format, benefits, and applications of CAS numbers, and how they help to organize and enhance the chemical information environment.

History of CAS numbers

The Chemical Abstracts Service (CAS) is a division of the American Chemical Society (ACS) that provides comprehensive and authoritative information on chemical substances and reactions. CAS was founded in 1907 as an index of chemical literature, and soon became the world’s largest and most trusted source of chemical information. In 1965, CAS introduced the CAS Registry system, a database of chemical substances that assigns a unique CAS number to each substance. The CAS Registry system was created to address the problem of inconsistent and ambiguous naming of chemical substances, which often resulted in confusion and errors among scientists and other users of chemical information. Since then, CAS numbers have become the global standard for identifying and indexing chemical substances, and are recognized by international organizations such as the World Health Organization (WHO), the International Union of Pure and Applied Chemistry (IUPAC), and the United Nations (UN).

Format of CAS numbers

A CAS number consists of three parts: a series of digits separated by hyphens, followed by a check digit in parentheses. For example, the CAS number of water is 7732-18-5. The first part of the CAS number can have from two to seven digits, depending on when the substance was registered. The second part has two digits, and the third part has one digit. The check digit is calculated by a formula that involves multiplying each digit by a weight factor and taking the sum modulo 10. The check digit helps to verify the validity and accuracy of the CAS number.

A CAS number has no inherent meaning or relation to the chemical structure or properties of the substance. It is simply a serial number that is assigned in sequential order when the substance is registered by CAS. However, a CAS number serves as a link to a wealth of information about the substance, such as its chemical name, structure, formula, physical and chemical properties, spectra, hazards, uses, suppliers, references, and more.

Benefits of CAS numbers

CAS numbers offer several advantages for identifying and accessing chemical information:

  • Uniqueness: CAS numbers ensure the uniqueness and unambiguous identification of chemical substances. This is particularly crucial when dealing with compounds with multiple common names or chemical formulas. Scientists can eliminate confusion and ensure accurate communication by assigning a distinct CAS number to each substance.
  • Universality: CAS numbers provide a standardized system for chemical identification that transcends language and regional variations. They are a common language for scientists worldwide, enabling effective communication, collaboration, and sharing of chemical information across borders.
  • Reliability: CAS numbers are assigned by trained experts at CAS who evaluate and verify the data submitted by the registrants. They also update the database regularly with new substances and information. Users can trust that the CAS numbers are accurate and authoritative.
  • Accessibility: CAS numbers serve as an efficient tool for locating and retrieving precise information about specific substances from extensive chemical databases. Prominent databases such as SciFinder, PubChem, Scopus, and others rely on CAS numbers as identifiers. Researchers can use these numbers to access detailed data, including chemical structures, physical properties, safety information, and references to scientific literature.

Applications of CAS numbers

CAS numbers have various applications in different fields and domains related to chemistry:

  • Research: CAS numbers help researchers to find relevant information about chemicals quickly and easily. They can use CAS numbers to search for literature, patents, spectra, reactions, synthesis methods, biological activities, and more. They can also use CAS numbers to compare and contrast different substances based on their properties and behaviors.
  • Regulation: CAS numbers help regulators to monitor and control the production, distribution, use, and disposal of chemicals. They can use CAS numbers to identify hazardous substances, enforce safety standards, track inventories, report incidents, and implement regulations. For example, the U.S. Environmental Protection Agency (EPA) uses CAS numbers for its Toxic Substances Control Act (TSCA) Inventory, which lists all existing chemical substances manufactured or processed in the U.S.
  • Industry: CAS numbers help manufacturers and suppliers to manage their chemical products efficiently and effectively, especially with the help of Safety Data Sheets (SDSs). They can use CAS numbers to label their products, communicate with customers, comply with regulations, obtain quality certificates, order raw materials, and market their products. For example, the European Chemicals Agency (ECHA) requires all substances placed on the European Union (EU) market to have a registration number under its Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) regulation, which often includes the corresponding CAS number.

CAS numbers are important because they provide a unique, universal, reliable, and accessible way to identify and access information about chemical substances. CAS numbers help to organize and enhance the chemical information environment, and have various applications in research, regulation, industry, and other domains related to chemistry. CAS numbers are assigned by the Chemical Abstracts Service (CAS), a division of the American Chemical Society (ACS), which is the world’s largest and most trusted source of chemical information.



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