Isometric certificate-of-analysis document with placeholder rows, a seal, and field icons for molecular structure, weight, HPLC peak, and magnifier
Mindful Research

Reading a Peptide Spec Sheet: CAS, MW, Formula, and Purity

Updated By: Mindful Research Team2 min read

Key takeaways

  • A peptide spec sheet confirms identity and quality through CAS number, molecular formula, molecular weight, and purity.
  • CAS number and molecular formula fingerprint the compound's identity.
  • Molecular weight drives concentration/molarity math and is what mass spectrometry confirms.
  • Purity (usually by HPLC) is the percentage that is the intended peptide.
  • All framing is laboratory and in vitro.

A peptide spec sheet identifies and verifies a research material through a few key fields: CAS number, molecular formula, molecular weight, and purity. This guide explains what each one tells you.

CAS number

The CAS Registry Number is a unique identifier for a chemical substance. It lets you confirm you have the exact compound the experiment calls for, independent of naming variations.

Molecular formula

The molecular formula lists the atoms that make up the peptide. It is the chemical-composition fingerprint used alongside molecular weight to confirm identity.

Molecular weight

Molecular weight (in daltons or g/mol) is essential for concentration math: converting a mass of peptide into molarity for an assay depends on it. It is also what mass spectrometry measures to confirm identity.

Purity

Purity is the percentage of the material that is the intended peptide, typically measured by HPLC. A higher, documented purity means fewer unknown species in your experiment.

Putting it together

Read together, these fields let a lab confirm identity (CAS, formula, MW), plan concentrations (MW), and judge quality (purity) before the peptide ever enters an assay. All of them appear on the Certificate of Analysis.

Find a COA: search every third-party lab report by product or batch number in our certificate of analysis library.

Related research guides

Research-use note

All peptides discussed are supplied for in vitro laboratory research use only.

Frequently asked questions

What is a CAS number on a peptide spec sheet?

A unique CAS Registry Number that identifies the exact chemical substance, independent of naming variations.

Why is molecular weight important?

It is required to convert a mass of peptide into molarity for assays, and it is the value mass spectrometry uses to confirm identity.

What does the purity percentage mean?

The percentage of the material that is the intended peptide, typically measured by HPLC; higher documented purity means fewer unknown species.

Where do these fields come from?

The Certificate of Analysis, which documents identity and quality for each batch. Reading a COA line by line

Research use only?

Yes, in vitro laboratory research use only.

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