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How to Read a Peptide Certificate of Analysis
A Certificate of Analysis (COA) is a lab-issued document describing tests performed on a specific batch of research material and the results those tests returned. Reading a COA well means separating what the paperwork actually establishes from what it does not.
This guide covers lot matching, HPLC purity, chemical identity and the analytical attributes a single test does, and does not, establish.
For laboratory research context only. PepDirect supplies research materials, not for human or veterinary use.
§ Definition
What is a Certificate of Analysis?
A Certificate of Analysis is documentation associated with a specific material and, more importantly, a specific lot or batch of that material. It records the tests that were performed on that lot, the analytical methods used and the results reported.
COAs are not standardised across every supplier. Two COAs from different labs may report different fields, use different methods and cover different attributes. A COA describes what was tested, not everything that could have been tested.
§ Lot matching
Why the lot number matters
The value of a COA depends on whether it corresponds to the actual lot supplied. A COA issued against a different batch tells you about that other batch, not the vial in your hand.
- The lot / batch number on the vial should be traceable back to the COA.
- A COA published without a lot reference is weaker documentation than one that specifies its batch.
- Where a supplier hosts a searchable library, matching the printed lot to the library entry closes the loop between physical material and documented testing.
PepDirect research materials publish lot-specific documentation. Verify the printed lot against the COA Library and, where offered, the batch-verification page before accepting the paperwork at face value.
§ HPLC purity
Understanding HPLC purity
HPLC stands for High-Performance Liquid Chromatography. It separates a sample into peaks based on how components interact with a chromatographic column, and chromatographic purity is generally reported from the relative peak areas.
The main peak represents the principal component detected under the stated method. Smaller peaks may represent impurities, degradation products or other detected species. A purity result is defined by the method used, different columns, gradients and detectors can produce different numbers on the same sample.
- HPLC purity ≈ percentage of the total detected signal attributable to the principal peak.
- The number depends on the specific analytical method, a higher figure under a less sensitive method is not automatically stronger.
- 'Purity' here means chromatographic purity of the detected components, not total mass purity of the vial.
§ Purity vs identity
Purity is not identity
Two separate questions live inside a COA. Purity asks: how much of the detected material corresponds to the principal chromatographic component? Identity asks: is that principal component actually the intended compound?
Confirming identity typically involves methods such as mass spectrometry, amino-acid analysis or reference-standard comparison. A high HPLC purity result on its own confirms that the sample is chromatographically clean, it does not, by itself, prove that the main peak is the intended peptide.
§ COA fields
What else might a COA include?
- Compound name and identifier(s)
- Lot / batch number and test date
- Assay / purity result and the analytical method used
- Chemical identity data (e.g. mass-spectrometry mass, sequence reference)
- Appearance
- Storage and handling notes
- Analyst / laboratory signature or reference
Exact fields depend on which tests were performed and what the issuing laboratory chose to report. Missing fields do not automatically mean the attribute is bad, they mean it was not tested or not reported here.
§ Limits
What a COA does NOT automatically prove
A single test result establishes what that test measured. It does not establish attributes the paperwork did not cover.
- 99%+ HPLC purity does not automatically mean 99% peptide by total vial mass, vial contents include salts, counter-ions, residual solvents and moisture unless separately quantified.
- HPLC purity does not automatically confirm chemical identity, that requires appropriate identity testing.
- A COA is not a sterility certificate unless a validated sterility test was performed.
- A COA is not an endotoxin certificate unless a validated endotoxin (e.g. LAL) test was performed.
- A COA does not establish biological activity or suitability for any human use.
§ Where to find them
How PepDirect uses lot-specific documentation
PepDirect research materials publish lot-specific analytical documentation where available. Users should match the lot number displayed on the product to its corresponding record in the COA Library.
PepDirect does not represent any research material as sterile, endotoxin-tested, sequence-confirmed or otherwise fit for human administration unless the specific documentation for that batch establishes that attribute.
§ Research product
Browse the COA Library
Every published lot number links to its analytical documentation. Match the lot printed on your vial to its COA entry before accepting purity or identity paperwork at face value.
§ References
Selected research references
- ICH Q6A, Specifications: Test Procedures and Acceptance Criteria for New Drug Substances (regulatory reference for analytical documentation)ICH
- USP <621>, Chromatography (reference for HPLC methods)United States Pharmacopeia
- Mass-spectrometry-based peptide identity confirmation, analytical reviewPubMed · Domon & Aebersold
§ FAQ
Frequently asked questions
- What does COA stand for?
- Certificate of Analysis, a document issued by a laboratory summarising the tests performed on a specific batch of material and the results reported.
- What does HPLC purity mean?
- It is chromatographic purity: the percentage of the total detected chromatographic signal attributable to the principal peak, under a stated analytical method.
- Does 99% HPLC purity mean the vial contains exactly 99% peptide by weight?
- No. HPLC purity is a chromatographic ratio of detected peak areas, not a mass balance of the whole vial. Total vial mass also includes salts, counter-ions, residual solvents and moisture unless separately quantified.
- Does HPLC prove peptide identity?
- Not on its own. HPLC purity establishes that the sample is chromatographically clean under the stated method. Confirming chemical identity typically requires additional testing such as mass spectrometry, amino-acid analysis or reference-standard comparison.
- Does a COA prove a material is sterile or endotoxin-free?
- Only if the COA reports the results of a validated sterility or endotoxin test. A COA does not automatically establish either attribute, testing must be specifically listed.
- Why should the COA lot number match the product lot number?
- Because a COA describes one specific batch. A generic COA that cannot be traced to the batch supplied describes another material, not the one in your hand.
- Where can I find PepDirect COAs?
- In the PepDirect COA Library, indexed by lot number. Every research material page links to the corresponding analytical documentation where it is published.
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