A short guide to CAS registry numbers, molecular formulas, and the other identifiers that confirm what a compound actually is.
When you look at a well-documented research compound, you will see a set of identifiers: a CAS number, a molecular formula, a molecular weight, and sometimes alternate names. These are not decoration. They are the fixed, verifiable identity of the molecule, and knowing how to read them lets you confirm you are looking at the compound you think you are. This article explains the main identifiers and how to use them.
What a CAS number is
A CAS Registry Number is a unique identifier assigned to a chemical substance by the Chemical Abstracts Service. Every distinct compound has its own CAS number, formatted as digits separated by hyphens, for example 137525-51-0. Because the number is unique and standardized, it removes ambiguity that names alone can create. A single compound might be sold under several names, but it has only one CAS number.
If you want to confirm two products are the same compound, comparing CAS numbers is more reliable than comparing names.
Molecular formula
The molecular formula lists the atoms that make up the molecule and how many of each, such as C62H98N16O22. For peptides, these formulas are large, but they serve the same purpose as for any molecule: they describe the exact atomic composition. A matching molecular formula is another confirmation of identity.
Molecular weight
The molecular weight is the mass of the molecule, usually given in grams per mole. On a Certificate of Analysis, molecular weight is often confirmed by mass spectrometry: the measured mass should match the known theoretical weight for the compound. This is a core identity check, because a mass that does not match signals that the sample is not what it claims to be.
For very large or complex peptides, a single published molecular weight can vary slightly by source, so these are sometimes given as approximate values.
Alternate names and development codes
Many research compounds carry more than one name. A compound might have a common name, a systematic name, and a development code from its research history. These alternate names are useful for cross-referencing literature and supplier documentation, but they are not a substitute for the CAS number when confirming identity.
How to verify a compound’s identity
Putting the identifiers together, a simple verification approach is:
- Start with the CAS number. It is the least ambiguous identifier. Confirm it matches across the product listing, the documentation, and any reference you are checking against.
- Cross-check the molecular formula and weight. These should be consistent with the compound the CAS number identifies.
- Look at the Certificate of Analysis. A COA that confirms identity by mass spectrometry ties the physical material in the vial back to these theoretical identifiers.
When the CAS number, molecular formula, molecular weight, and COA identity results all agree, you have strong confirmation of what the compound is.
The takeaway
CAS numbers and the identifiers around them are the fixed identity of a compound, and they let you verify a material rather than take a name on faith. A supplier that publishes these identifiers, and backs them with a Certificate of Analysis, is giving you the tools to confirm exactly what you are buying.
Meridian Research Co. publishes CAS numbers, molecular data, and third-party certificates of analysis for its compounds. All products are for laboratory research use only and are not for human or veterinary use.