CAS Number- What is it?

CAS Numbers – What are they?

The CAS registry is a vast collection of chemical substance information which contains more than 60 million organic and inorganic substances. The CAS number or CAS Registry Number is:

CAS Number1. A unique numeric identification

2. Identifies only one substance

3. Is a link to a large amount of information on a substance.

A CAS number is a unique chemical identfier that may contain up to 10 numbers and is divided into 3 parts by hyphens.  The right-most digit is a check digit used to verify the validity of the entire number.  A CAS number is assigned to a substance when it enters the CAS registry database (which is typically when a new chemical entity (or NCE) is published in the open scientific literature). CAS numbers are assigned to new substances in sequential order.  New discovery compounds that are very early in the development pipeline are likely not to have a CAS number till they are published in the scientific literature.  When Affygility Solutions performs potent compound safety categorization for an active pharmaceutical ingredient, while we don’t need a specific CAS number, having one makes it is useful for performing literature searches.

CAS Numbers – Why do regulatory agencies rely on them?

Since CAS registry numbers do not rely on the naming of a substance, scientists, industrial hygienists, and environmental, health and safety professionals rely on them to distinguish between different nomenclature for a particular substance.  For instance, ethanol has many synonyms, and all these names would be mistaken as different substances without the CAS Number.   The CAS Number also serves to bridge the language gap among different countries because it does not depend on the naming of the substance but rather a numerical identification.  Government agencies use CAS registry numbers to keep track of all substances because they are unique, they can be validated quickly and effectively, and they are internationally recognized. A chemical substance can be described in many different ways, but with a CAS number all chemicals can be identified as unique because they have a different number assigned to them.

The CAS Number can also be used to distinguish between the stereoisomers of a compound. For instance, Glucose, a sugar molecule has two forms, D-Glucose and L-Glucose.  D-Glucose is assigned CAS Number 50-99-7 and L-Glucose is assigned CAS Number 921-60-8.

In addition to scientific journals, CAS numbers are often used in scientific reference publications such as Sax’s Dangerous Properties of Industrial Materials, or Goodman and Gilman’s The Pharmacological Basis of Therapeutics.


The CAS Number is a useful way for scientists and regulatory agencies to easily distinguish between different substances.  The CAS registry is the most comprehensive collection of chemical substance information in the world with more than 60 million organic and inorganic substances.  CAS Numbers can be useful to distinguish among similar chamicals and aid regulatory agencies in keeping track of disclosed substances.

If you have any questions about potent compound safety, industrial hygiene, occupational toxicology or containment validation, contact the experts at Affygility Solutions.


About Dean Calhoun

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Dean is the President and CEO of Affygility Solutions. Affygility Solutions provides environmental, health and safety software, potent compound safety, industrial hygiene, containment validation services to the pharmaceutical, biotechnology, and medical device industry. "Dean's Google+ Profile"

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