What is a CAS Number?

A CAS Registry Number is a unique numerical identifier assigned by the Chemical Abstracts Service to every chemical substance described in the open scientific literature. It is the global standard for identifying chemicals unambiguously across languages and suppliers.

tip

CAS numbers are the global standard for identifying chemical substances — a single number means the same chemical in every language.

Structure of a CAS Number

A CAS number has three parts separated by hyphens, for example 62-53-3 (aniline):

Part Meaning Example
First Registry segment 62
Second Compound descriptor 53
Third Check digit 3 
def parse_cas(cas: str) -> list[int]:
    return [int(part) for part in cas.split("-")]

Why It Matters in Sourcing

When you request a quote, always confirm the CAS number with your supplier:

warning

Never rely on the product name alone — the same name can refer to different grades or isomers.

Verification Workflow

  1. Search the registry for the CAS number.
  2. Compare the molecular formula.
  3. Request the SDS and CoA from the supplier.

Summary

CAS numbers remove ambiguity from chemical sourcing. Always quote them in RFQs, orders and shipping documents.[1]

  1. See the American Chemistry Council’s guidance on chemical identifiers for further reading. ↩︎