CAS Numbers · Compound Identification · Quality Assurance · Research Methods
CAS Registry Numbers: Why They Matter for Research Compound Identification
Pepterna Research Team, Research & Compliance · June 1, 2026 · 4 min read
What CAS numbers are, how they work, and why verifying them is critical when sourcing research-grade compounds.
CAS Registry Numbers: Why They Matter for Research Compound Identification
The CAS (Chemical Abstracts Service) Registry Number is a unique numerical identifier assigned to every chemical substance described in the open literature. For researchers sourcing compounds, CAS numbers are the most reliable way to confirm you are purchasing the correct material.
What Is a CAS Number?
Administered by the American Chemical Society's Chemical Abstracts Service, CAS Registry Numbers are assigned sequentially as new substances are identified. The format is three groups of digits separated by hyphens (e.g., 137525-51-0). Each number maps to one specific chemical substance with a defined molecular structure.
As of 2026, the CAS Registry contains over 230 million unique chemical substances.
Why CAS Numbers Matter
**Unambiguous identification** — Chemical names can vary (common names, IUPAC names, brand names, abbreviations), but a CAS number always refers to one specific substance. "BPC-157", "Body Protection Compound 157", and "PL 14736" all refer to CAS 137525-51-0.
**Cross-referencing** — CAS numbers allow you to look up a compound in databases like PubChem, ChemicalBook, SciFinder, and the CAS Common Chemistry database to verify its properties independently.
**Literature searching** — Including CAS numbers in literature searches returns more precise results than name-based searches, which may return unrelated compounds with similar names.
**Quality verification** — Comparing the CAS number on a Certificate of Analysis against the expected CAS number for a compound is a basic but important quality check.
Common Pitfalls
**Salt forms** — A compound and its salt forms (acetate, hydrochloride, TFA) may have different CAS numbers. Verify that the CAS number matches the specific form you need.
**Stereoisomers** — Enantiomers and other stereoisomers have distinct CAS numbers. The L- and D- forms of a peptide are different substances.
**Obsolete or duplicate entries** — Occasionally, a substance may have been assigned multiple CAS numbers historically. The CAS Common Chemistry database can help resolve these.
At Pepterna
Every Pepterna product page lists the CAS Registry Number alongside the compound name, sequence (for peptides), molecular formula, and molecular weight. CAS numbers are verified against the Certificate of Analysis for each batch.
All products are sold for research use only. Not for use in humans or animals.