How to Read a Certificate of Analysis

A Certificate of Analysis (COA) is a document from an analytical testing laboratory certifying the composition of a specific batch of material. For research peptides, a COA should confirm identity, purity, and the absence of specified contaminants. Knowing how to read one — and how to tell a real one from a decorative PDF — is essential for any serious researcher evaluating a supplier.

COA vs. Certificate of Conformance — Not the Same Thing

A Certificate of Conformance (COC) is a supplier's written claim that a product meets a specification — it does not have to include any actual test data. A Certificate of Analysis (COA) is different: it reports the real, measured results from an actual analytical run — specific HPLC peak areas, a specific purity percentage, a specific mass-spec reading — tied to a specific lot. If a document only states that a product 'meets specifications' without showing measured values, a lot number, and a testing date, it's functioning as a COC, not a COA, regardless of what it's labeled.

What a COA Should Contain

1. Testing laboratory name and accreditation

The COA should originate from an independent third-party laboratory, not the supplier's internal QC team. Look for ISO/IEC 17025 accreditation, the international standard for testing and calibration laboratory competence, or an equivalent regional accreditation. The lab name, address, and ideally an accreditation number should be present and independently checkable against the accrediting body's public registry.

2. Lot number

This is the most important field to verify. The lot number on the COA must match the lot number printed on your vial label exactly. A COA without a matching lot number is essentially worthless — it may belong to a different batch entirely, possibly a cleaner one used to represent every batch a supplier sells.

3. HPLC purity

Expressed as a percentage (e.g., ≥98% by HPLC). This value represents the proportion of the target compound relative to all UV-absorbing material in the sample. See our peptide purity standards article for a detailed explanation of how this figure is actually calculated from a chromatogram.

4. Mass spectrometry (MS) identity confirmation

Mass spec confirms the molecular weight of the compound, verifying that you have the correct compound — not just any high-purity material. For peptides, this is a meaningful additional test beyond purity alone: a sample can be 99% pure and still be the wrong compound if it was never sequence-confirmed.

5. Heavy metals panel (optional but preferred)

Testing for arsenic, lead, cadmium, and mercury. Standard thresholds follow USP <232>/<233> or ICH Q3D guidelines for elemental impurities. Not all COAs include this — it's a premium test that adds credibility, and its absence isn't automatically disqualifying, but its presence is a meaningful positive signal.

6. Testing date and reference to method

A COA should be dated, and ideally cite the analytical method used (e.g., 'RP-HPLC, USP <621>' or an internal method reference). A COA with no date, or one that appears to have been reused across multiple product listings for years, is a red flag on its own.

Reading the Chromatogram Itself

If the COA includes the actual HPLC chromatogram image (not just the summary purity number), look for a single dominant, sharp peak with a clean baseline before and after it. Small shoulder peaks near the main peak typically represent truncated or deletion sequences from synthesis — some amount is normal and accounted for in the purity percentage, but a chromatogram with several similarly-sized peaks alongside the 'main' one is inconsistent with a high purity claim and worth questioning directly with the supplier.

Red Flags to Watch For

• No lab name, or only the supplier's own internal testing listed
• Lot number missing or not matching the product label
• Purity listed without specifying the analytical method used
• No date on the analysis — COAs should be from the current production year
• A single generic COA used across multiple products or lots
• A 'Certificate of Conformance' presented as if it were a COA — no actual measured data shown

Verifying Your Lot

Always verify the lot number against the supplier's documentation before using a compound in research. You can verify any lot we ship using our Verify page — enter the lot number from your vial label to pull the COA for that exact batch.

Research Use Only

This guide is provided for research and educational purposes. All compounds referenced across our catalog are for research use only and are not intended for human consumption.