How to Read a Peptide Certificate of Analysis
A certificate of analysis is only useful if you can tell a real one from a decorative one. This guide walks each section of a research peptide COA and explains what the numbers actually establish about the vial in front of you.
Updated August 8, 2026
The header: what the document is claiming
The top of a valid COA names the compound, the lot or batch number, the quantity per vial, the date of analysis, and the laboratory that performed it. If the lot number is missing, the document cannot be tied to your vial and proves nothing. If the analysis date is missing, you cannot tell whether the report predates the material it supposedly describes.
- Compound name and sequence or CAS reference
- Lot or batch number matching the vial label
- Date of analysis, not just a date of issue
- Name of the independent laboratory and its contact detail
HPLC: what the purity number means
Read the chromatogram, not the headline
High-performance liquid chromatography separates the sample over time and plots detector response. Purity is reported as the target peak's area as a percentage of total peak area. A bare '99%' with no trace behind it is an assertion. The chromatogram shows whether that 99% sits under one sharp peak or is being propped up by an integration window that swallowed shoulders.
What impurity peaks tell you
Small peaks eluting close to the main peak are usually synthesis-related: deletion sequences, incomplete deprotection, or oxidation products. Their presence is normal. Their size, and whether they are consistent across lots, is the signal worth tracking.
Mass spectrometry: identity, not purity
HPLC tells you how much of the sample is one thing. Mass spec tells you whether that thing is the compound you ordered. The observed molecular weight should match the theoretical weight for the sequence within the instrument's stated tolerance. A COA with purity data and no identity data has skipped the more important question.
The secondary panels
- Water content by Karl Fischer — affects the true peptide mass in the vial
- Acetate or TFA counter-ion content — part of the net peptide calculation
- Net peptide content — the fraction of vial mass that is actually peptide
- Sterility and endotoxin where the format calls for it
- Appearance and solubility notes
Red flags that justify rejecting a supplier
- One COA reused across every product or every lot
- A flattened image with no chromatogram or instrument metadata
- Purity stated without a method
- A lot number on the document that does not appear on the vial
- No named laboratory, or a laboratory that is the seller itself
How our documentation is structured
Each lot we list carries its own third-party report with the chromatogram, the mass spec trace, and the lot reference that is printed on the vial and recorded in your order history. You can look up a batch directly rather than taking a product page's word for it.
All compounds are sold strictly for laboratory research and development. They are not for human or veterinary use, and nothing on this page is medical advice.
Frequently asked questions
- Does a high HPLC purity number guarantee the right compound?
- No. HPLC measures how much of the sample is a single species; mass spectrometry establishes that the species is the intended compound. A complete COA includes both.
- What is net peptide content?
- The share of the vial's mass that is peptide rather than water and counter-ion salts. It matters because concentration calculations based on gross vial mass will otherwise overstate the peptide present.
- Should every lot have its own COA?
- Yes. A per-lot report is the only way an analysis describes the material you received. A single reused document tells you nothing about a later batch.
- Can I verify a batch number against your records?
- Yes. Batch numbers appear on the vial label and in your order record, and each maps to the analytical report for that specific lot.
