Laboratory glossary
CAS numbers: identity and traceability limits
An identifier for an entity in the CAS Registry; it does not independently describe purity, batch or commercial quality.
Source editorial review:
The distinction that matters
A similar commercial name does not justify assigning another chemical form’s CAS number.
What a CAS number is
A CAS Registry Number identifies a substance recorded by Chemical Abstracts Service. It consists of three hyphen-separated numeric blocks; the last digit is a check digit derived from the preceding digits to help detect transcription errors.
The identifier does not encode structure, formula, mass or chemical family. Its value is as a stable registry key: catalogs using different common, systematic or commercial names can still refer to the same registered substance.
Registration concerns substance identity rather than package size. A free compound and a separately registered salt form may have different identifiers even when routine laboratory speech uses the same abbreviated name.
Why it matters in a research catalog
Peptide nomenclature can involve a development code, acronym, long systematic name and commercial synonyms for one material. Name-only searches can miss relevant records or mix related compounds. An appropriate CAS number offers a more specific search key.
When comparing suppliers, check the registry identity before comparing purity, presentation or price. Otherwise two related but distinct substances may be treated as equivalent.
- An analog or fragment is a distinct substance and may have its own CAS registration. A shared name root does not imply a shared identifier.
- Equal masses of free and salt forms do not necessarily provide equal net peptide quantities, because counterions contribute mass. The declared form and content basis remain important.
- Some recently investigated substances lack an assigned CAS number. Absence alone does not disprove identity; a complete sequence and analytical documentation remain essential.
Practical use in records
Recording CAS number together with batch identification can make material identity more robust to name changes and staff turnover. It complements a readable compound name rather than replacing batch traceability.
It is also useful when retrieving safety data sheets and third-party handling information. Check that the retrieved document matches the intended form; neither a familiar name nor an unverified copied identifier is sufficient.
Verify the check digit when entering inventory data. A transcription error may produce an invalid number or point to another substance. Storage requirements and analytical specifications must still come from the relevant documentation; they cannot be decoded from the CAS number.
Common confusion
CAS, SKU and batch identifiers have different roles. CAS concerns substance identity; a supplier’s catalog number identifies a commercial product; a batch number identifies a particular production. One substance can appear in many presentations and batches. Molecular mass is also different: it is calculated from composition and is not unique, whereas a CAS number is an assigned identifier without an encoded chemical meaning.
How to record it
CAS checked against name, structure or sequence and declared form.