How to Read a Certificate of Analysis

What Is a Certificate of Analysis?

A Certificate of Analysis (COA) is a document issued by a laboratory that summarizes the analytical testing performed on a specific batch of product. For research peptides, a COA provides objective, third-party evidence of the peptide's identity, purity, and quality.

Every reputable peptide supplier provides COAs for each product. If a supplier cannot or will not provide a COA, that is a disqualifying red flag — there is no substitute for independent analytical verification.

Anatomy of a COA

A complete peptide COA contains several standard sections. Understanding each section allows you to evaluate whether the peptide meets the quality standards required for your research.

Product Identification

Field	What It Tells You
Product Name	The peptide (e.g., BPC-157, Semaglutide, Tirzepatide)
Batch Number	Unique identifier for this production run.
Molecular Formula	Chemical composition (e.g., C62H98N16O22 for BPC-157)
Molecular Weight	Expected molecular mass. Used to verify identity via mass spectrometry.
Sequence	The amino acid sequence in single-letter or three-letter code.
Quantity	Net peptide content per vial (e.g., 5mg).
Appearance	Physical description (typically "white to off-white lyophilized powder").

Purity Analysis

The purity section is the most important part of the COA. It tells you how much of the sample is actually the target peptide versus impurities.

HPLC Purity

Reported as a percentage (e.g., 99.2%). This value comes from High-Performance Liquid Chromatography analysis. The chromatogram should be included — either embedded in the COA or available as a separate document.

Purity Level	Quality Assessment	Typical Use
>99%	Exceptional	Demanding research applications
98-99%	High quality	Standard research grade
95-98%	Acceptable	Preliminary screening
<95%	Low quality	Not recommended for most research

Identity Confirmation

Mass Spectrometry (MS)

Mass spectrometry measures the molecular weight of the peptide. The observed mass should match the theoretical (calculated) mass within an acceptable tolerance.

Field	What To Check
Observed MW	The measured molecular weight from the mass spectrum
Theoretical MW	The calculated molecular weight based on the amino acid sequence
Mass accuracy	The difference between observed and theoretical. The values should be close — minor variations are normal due to instrument calibration and ionization conditions.

If the observed mass deviates significantly from the theoretical mass, the sample may contain the wrong peptide, a modified version, or a degradation product.

Types of Mass Spectrometry

• ESI-MS (Electrospray Ionization) — Most common for peptides. Shows multiple charge states. Good for peptides up to ~6,000 Da.
• MALDI-TOF (Matrix-Assisted Laser Desorption/Ionization) — Produces a single peak at the molecular ion. Better for larger peptides and proteins.
• LC-MS — Combines HPLC separation with MS detection. The most comprehensive single analysis.

Additional Quality Tests

Beyond purity and identity, some COAs include additional testing. These are not always required but indicate thorough quality control.

Test	What It Measures	Acceptable Result
Sterility	Microbial contamination	No growth detected
Water content (Karl Fischer)	Residual moisture in lyophilized product	<5%
Amino acid analysis (AAA)	Quantitative amino acid composition	Ratios match theoretical sequence
Net peptide content	Actual peptide weight excluding salts, water, counterions	Varies by product (typically 60-85% of gross weight)
Counterion content	TFA or acetate salt percentage	Reported for accurate concentration calculations

Third-Party vs. In-House Testing

COAs can come from two sources: the manufacturer's own laboratory (in-house) or an independent testing laboratory (third-party). The distinction matters.

Third-Party Testing

• Performed by an independent, accredited laboratory with no financial relationship to the manufacturer
• Results are unbiased — the lab has no incentive to report favorable numbers
• The COA should identify the testing laboratory by name
• Look for ISO 17025 accreditation or equivalent quality standard

In-House Testing

• Performed by the manufacturer's own QC laboratory
• Can be accurate but lacks independent verification
• Conflict of interest exists — the manufacturer benefits from reporting high purity
• Acceptable as supplementary data, but should not be the sole source of quality evidence

Red Flags on a COA

• No chromatogram or mass spectrum included — just a purity number without supporting data
• Generic or templated document — identical formatting across all products may indicate fabricated data
• 100.0% purity reported — analytically implausible; even pharmaceutical-grade peptides have trace impurities
• No testing laboratory identified — anonymous testing cannot be verified
• Date mismatch — a COA dated significantly before the product's manufacture date
• Missing method details — column type, mobile phase, flow rate should be documented
• Molecular weight mismatch — observed MW should be close to theoretical; minor variations are normal, but large deviations warrant investigation

How to Verify a COA

1. Check the molecular weight — observed vs. theoretical should agree within 0.1%
2. Review the chromatogram — look for a dominant main peak with a clean baseline
3. Confirm purity percentage — calculated from peak area integration on the chromatogram
4. Identify the testing lab — is it named? Is it independent?
5. Check the date — testing should be recent relative to the product's manufacture
6. Cross-reference with the product page — a reputable supplier makes COAs easily accessible. Heritage Labs publishes all COAs in our COA Portal.

Key Takeaways

• A COA is your proof of quality — no COA means no quality assurance
• HPLC purity >98% is research grade; >99% is exceptional
• Mass spectrometry confirms identity; HPLC confirms purity — both are needed
• Third-party testing from a named lab is the gold standard
• Always review the chromatogram, not just the reported number
• Red flags: missing data, 100% purity claims, anonymous testing