What is a CAS number, and how to use one to verify a compound
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A CAS Registry Number is a unique numeric identifier assigned to a single chemical substance, written as three groups of digits separated by hyphens. It lets a supplier, a vial label and a certificate of analysis refer to exactly the same material even when the names differ. This guide shows how to read one and uses examples from our listings.
CAS numbers at a glance
| Format | Up to ten digits in three groups, for example 70-18-8 |
|---|---|
| Last digit | A check digit calculated from the others |
| Assigned by | CAS, a division of the American Chemical Society |
| Identifies | One substance, regardless of name or abbreviation |
| Where to find it | Listing, vial label and certificate of analysis |
How is a CAS number structured?
The number has three parts. The first group has two to seven digits, the second has two digits, and the third is a single check digit. The check digit comes from a simple weighted sum of the other digits, so a mistyped number can often be spotted. Nothing in the number reveals the structure of the compound; it is a lookup key and nothing more.
What do real examples look like?
These numbers are taken from our listings.
| Compound | CAS number | Type |
|---|---|---|
| BPC-157 | 137525-51-0 | Pentadecapeptide |
| DSIP | 62568-57-4 | Nonapeptide |
| Glutathione | 70-18-8 | Tripeptide |
| GHK-Cu | 89030-95-5 | Copper-complexed tripeptide |
How do you use one to verify a compound?
Compare the number in three places: the product listing, the vial label and the batch certificate. All three should match. Then check that the name on each document is one of the synonyms for that number, since abbreviations vary between suppliers. If a listing leaves the number to the batch document, as some listings do, the certificate becomes the only reference and should be kept with the vial.
A CAS number identifies the substance, not the quality of the batch. Purity and mass come from the analytical results, which are covered in how to read a peptide certificate of analysis.
What should the documentation show?
- The CAS number matches the product listing and the vial label.
- The compound name is a recognised synonym for that number.
- The batch number on the certificate matches the vial.
- Purity and mass results are reported alongside the identifier.
Batch documents are on the COAs page. See also the supplier checklist.
Frequently asked questions
What does CAS stand for?
CAS stands for Chemical Abstracts Service, the division of the American Chemical Society that assigns the numbers.
Can two compounds share a CAS number?
No. Each number refers to a single substance, although a substance can have many names.
Does the CAS number tell you the purity?
No. It identifies the substance only. Purity is a property of the batch and is reported on the certificate of analysis.
What if a listing does not show a CAS number?
Check the batch certificate of analysis, which should state the identifier, and contact the supplier if it does not.
How many digits does a CAS number have?
Up to ten, arranged in three groups. The final group is a single check digit.
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The Ascend Research team