All you Need to Know About CAS Numbers

In the early 1900’, the American Chemical Society first published a Chemical Abstracts journal. The purpose of this journal was to help scientists benefit from the published work of their peers around the world by monitoring, indexing and abstracting the literature related to chemicals and chemistry around the world. Over the years, namely 1956, the Chemical Abstracts journal became Chemical Abstracts Service (CAS) and an American Chemical Society operating division. During this time, CAS has evolved into the world's authority for chemical information, providing the global scientific community access to the most current chemical and related scientific information available. This information was made immediately available through the databases such as CAS Registry and CAS References. Each chemical substance in the CAS registry is assigned a CAS Registry Number or CASRN, also referred to as CAS number. CAS numbers are unique numbers assigned to chemical substances by the Chemical Abstract Service to provide a consistent and reliable way of identifying the chemical substances. They are easily recognisable regardless of the country or region. 

The number is divided into three parts by hyphens and is up to ten digits long. The first part can have from two to seven digits, while the second always consists of two and the third always consists of only one digit, known as the check digit. With this current format, if we are to do a quick calculation, it would mean that there is a maximum of one billion unique CAS numbers available that can be dedicated to chemical substances. Since there is no real chemical significance to these sets of numbers, they are assigned in sequential order, meaning that the newer substances have larger numbers than the chemicals previously entered in the registry.

CAS Registry

As previously mentioned, the chemicals and their assigned CAS numbers are registered in the CAS registry. This centralised registry is updated daily with thousands of new substances. This makes the CAS registry one of the most authoritative databases for disclosed chemical substances.

CAS registry contains a wide variety of substances, including the world's most extensive collection of:

  • Organic and inorganic compounds
  • Metals and alloys
  • Minerals
  • Coordination compounds and Organometallics
  • Elements, Isotopes, and Nuclear particles
  • Proteins and nucleic acids
  • Polymers
  • Substances of unknown or variable composition and biologics (UVCBs)

The wide range of substance types that are being registered, coupled together with the fact that thousands of entries are made daily, resulted in CAS announcing that it had registered its 250 millionths unique chemical substance in April 2021.

Importance of CAS numbers

For chemicals around the globe, there have always been many different ways for a description of new and already existing chemical compounds, such as molecular formula, common names, IUPAC nomenclature, trade or shipping names and so on. Sometimes due to language barriers or differences occurring due to synonyms or other names, these descriptions could not immediately tell us what the substance is currently in question. An example could be a parody used to confuse the readers on social media platforms, involving water and its unfamiliar chemical name dihydrogen monoxide (DHMO) while also listing some of water's properties in a particularly threatening manner, such as accelerating corrosion (rust) and causing suffocation (drowning). This way, for a reader, the substance in question might not be immediately obvious. But by checking the CAS number or using it, it becomes unanimously clear that both terms share the same identifier (CAS number), hence are the same chemical. Since CAS numbers are unique for each chemical substance, they present an excellent resource for identifying chemicals. CAS numbers are the most commonly used unique substance identifiers.

This makes the CAS number almost an invaluable tool for chemists, scientists and any other person handling the chemical substances. It can quickly show users reliable and accurate information about the chemicals they are handling.

Lately, with the implementation of the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) worldwide, CAS numbers have also become a regulatory requirement. Today, Safety Data Sheets (SDS) need to have CAS numbers included since it is a requirement set up by the GHS. In the SDS, CAS number provides a safe way of identifying the chemical substance, reducing the confusion or mistakes that could occur due to the chemical substance having many different names, primarily if a person handles the chemical without a strong chemistry background.

With its introduction in the legislation, CAS numbers are recognised as a universal standard and embraced by both industry and regulatory agencies worldwide.

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