CAS Registry Numbers and What They Identify

A CAS Registry Number is a unique identifier assigned to a chemical substance. On a peptide certificate it is one of the few fields that is unambiguous, provided it is read for what it actually designates.

What the number identifies

A specific substance, defined by its structure — not a name, not a class, and not a product. The format is a string of digits in three groups, the last of which is a check digit calculated from the others, so a transposed digit usually produces an invalid number rather than a different valid one.

Because assignment is structural, distinctions that matter chemically each earn their own entry:

• Salt forms are separate. A peptide as the free base and the same peptide as its acetate or trifluoroacetate salt are different substances with different numbers. TFA and acetate counter-ions covers why the distinction affects the mass in the vial.
• Terminal modifications are separate. An amidated peptide and its free-acid counterpart have different numbers. Terminal modifications covers the one-dalton difference behind that.
• Complexes are separate. A peptide and its metal complex are distinct substances. GHK and GHK-Cu are the example in this catalogue, and the two registry numbers and what each mass refers to works through the arithmetic.
• Stereochemistry is separate where it is defined, so an enantiomer or a specified diastereomer carries its own entry.

Why one trade name can map to several numbers

Trade names are marketing designations and are not governed by structure. A name may be applied to a free base by one supplier and a salt by another, or — as happens with fragment products — to two materials whose masses differ by a factor of several. Thymosin beta-4 and the fragment covers that case.

Where a certificate carries a registry number, it resolves which substance was characterised in a way a trade name cannot. Where it carries only a trade name, the measured mass is the field that does that work.

What the number does not carry

It says nothing about purity, nothing about the batch, nothing about who made it and nothing about quality of any kind. Two materials sharing a registry number can differ substantially in everything a purity test measures. The number establishes what the substance is supposed to be, and the rest of the document establishes what arrived.

Registration is also not approval. A CAS number is an index entry, and having one carries no regulatory implication whatsoever. Regulatory status of research peptides in Canada covers that ground.

All material is supplied for laboratory research use only. It is not a drug, not a supplement, and not for use in humans or animals.