CAS Registry Number

November 30, -0001, 12:00 371

CAS Registry Number

CAS Registry Number, also referred to as CASRN or CAS Number, is a unique numerical identifier assigned by the Chemical Abstracts Service (CAS) to every chemical substance described in the open scientific literature (currently including all substances described from 1957 through the present, plus some substances from the early or mid 1900s), including organic and inorganic compounds, minerals, isotopes, alloys and nonstructurable materials (UVCBs, of unknown, variable composition, or biological origin).

The Registry maintained by CAS is an authoritative collection of disclosed chemical substance information. It currently identifies more than 129 million organic and inorganic substances and 67 million protein and DNA sequences, plus additional information about each substance. It is updated with around 15,000 additional new substances daily.

Use

Historically, chemicals have been identified by a wide variety of synonyms. Frequently these are arcane and constructed according to regional naming conventions relating to chemical formulae, structures or origins. Well-known chemicals may additionally be known via multiple generic, historical, commercial, and/or (black)-market names.

CAS Registry Numbers are simple and regular, convenient for database searches. They offer a reliable, common and international link to every specific substance across the various nomenclatures and disciplines used by branches of science, industry, and regulatory bodies. Almost all molecule databases today allow searching by CAS Registry Number.

On the other hand, CASRNs are not related to chemistry, are proprietary and unrelated to any previous systems, and do not readily form phonetic analogs or synonyms.

Format

A CAS Registry Number has no inherent meaning but is assigned in sequential, increasing order when the substance is identified by CAS scientists for inclusion in the CAS REGISTRY database.

A CASRN is separated by hyphens into three parts, the first consisting from two up to seven digits,[5] the second consisting of two digits, and the third consisting of a single digit serving as a check digit. This current format gives CAS a maximum capacity of 1,000,000,000 unique identifiers.

The check digit is found by taking the last digit times 1, the previous digit times 2, the previous digit times 3 etc., adding all these up and computing the sum modulo 10. For example, the CAS number of water is 7732-18-5: the checksum 5 is calculated as (8×1 + 1×2 + 2×3 + 3×4 + 7×5 + 7×6) = 105; 105 mod 10 = 5.

Granularity

  • Stereoisomers and racemic mixtures are assigned discrete CAS Registry Numbers: L-epinephrine has 51-43-4, D-epinephrine has 150-05-0, and racemic DL-epinephrine has 329-65-7
  • Different phases do not receive different CASRNs (liquid water and ice both have 7732-18-5), but different crystal structures do (carbon in general is 7440-44-0, graphite is 7782-42-5 and diamond is 7782-40-3)
  • Commonly encountered mixtures of known or unknown composition may receive a CASRN; examples are Leishman stain (12627-53-1) and mustard oil (8007-40-7).
  • Some metals are discerned by their oxidation state, e.g. the element chromium has 7440-47-3, the trivalent Cr(III) has 16065-83-1 and the hexavalent Cr(VI) ion has 18540-29-9.
  • Occasionally whole classes of molecules receive a single CASRN: the class of enzymes known as alcohol dehydrogenases has 9031-72-5.

Type of substances

CAS REGISTRY contains a wide variety of substances, including the world's largest collection of:

  • Organic compounds
  • Inorganic compounds
  • Metals
  • Alloys
  • Minerals
  • Coordination compounds
  • Organometallics
  • Elements
  • Isotopes
  • Nuclear particles
  • Proteins and nucleic acids
  • Polymers
  • Nonstructurable materials (UVCBs)

 

References

  1. CAS registry description, by Chemical Abstracts Service
  2. American Chemical Society. "CAS Registry and CASRNs".
  3. Chemical Substances - CAS REGISTRY
  4. https://www.cas.org/content/chemical-substances/faqs
  5. https://www.spectrumchemical.com
  6. https://en.wikipedia.org/wiki/CAS_Registry_Number