US Peptide Science Research Team
August 24, 2026
Researchers evaluating peptide quality depend on Certificates of Analysis (COAs) to verify compound identity and purity. However, not all COAs carry equal evidentiary weight. A third-party COA produced by an independent analytical laboratory—one with no financial stake in the result—provides credibility that in-house manufacturer testing cannot match.
evopeak.io defines third-party testing as analysis performed by a laboratory independent of the peptide supplier: "The independence is what gives the test its evidential value: an independent laboratory has no incentive to produce favourable results and applies its standardised methods regardless of who the client is."
This distinction is foundational. A manufacturer's self-declared COA is not third-party verification; it is a vendor claim. True third-party analysis means the testing laboratory is operationally and financially separate from the supplier, applies standardized analytical protocols, and maintains accreditation that demonstrates laboratory competence.
Every credible peptide COA must answer two distinct questions:
High-performance liquid chromatography (HPLC) separates compounds in a sample and quantifies what fraction is the target peptide versus impurities. The result is expressed as area-percent purity—a percentage representing the chromatographic signal of the target compound relative to all signals detected.
lifelinkresearch.com clarifies the distinction: "HPLC measures what percentage of the material in the vial is the intended peptide versus everything else — synthesis byproducts, deletion sequences, oxidized forms, counter-ions, and residual reagents."
A complete HPLC result includes:
Mass spectrometry (MS) measures the mass-to-charge ratio (m/z) of ionized molecules and reconstructs the molecular mass. For peptides, electrospray ionization (ESI-MS) is the standard method. The measured molecular mass is compared to the theoretical mass calculated from the intended amino acid sequence.
A match within ±1 Da (Dalton) confirms the compound is the correct peptide. evopeak.io explains: "For peptides, electrospray ionisation (ESI-MS) is standard, producing multiply charged ions that allow the full molecular mass to be calculated from the m/z values of different charge states."
Critically, MS identity confirmation answers what the compound is, not what it contains. Routine MS analysis does not reveal detailed sequence confirmation (requiring specialized MS/MS fragmentation), stereochemical purity (D vs. L amino acids), or post-translational modification status.
lifelinkresearch.com notes: "For a peptide, the key number is the observed monoisotopic mass (or average mass, depending on the instrument settings). This should match the theoretical mass for the peptide sequence within the instrument's mass accuracy (typically ±0.5 Da or ±0.01%)."
Why both are required: HPLC without MS tells you the sample is pure but not whether it is the correct compound. MS without HPLC tells you the right compound is present but not whether impurities or degradation products are also present. Together, they answer the two fundamental quality questions.
The testing laboratory must be independently verifiable. peptidetrust.org provides a practical verification framework:
ISO/IEC 17025 is the international standard for testing and calibration laboratory competence. Accredited laboratories demonstrate quality management system controls, proficiency testing, and regular audits. Accreditation does not guarantee a favorable result—it demonstrates that the laboratory applies consistent, documented methodology.
peptigrity.com emphasizes: "ISO/IEC 17025:2017 is the international standard for the general requirements of testing and calibration laboratories — the global benchmark for analytical lab competence across pharmaceutical, environmental, food safety, and forensic applications."
Critically, ISO 17025 accreditation is specific to the test methods and matrices listed in the laboratory's scope of accreditation. A lab accredited for heavy metals analysis is not automatically accredited for peptide purity by HPLC. When reviewing a COA, verify that the laboratory holds ISO 17025 accreditation specifically for peptide HPLC purity and LC-MS identity testing. This information should be visible on the laboratory's website or in the COA header, and the scope of accreditation document should explicitly list the test methods and matrices.
The COA header should include the laboratory's name, address, phone number, and website. If the testing laboratory cannot be independently identified through an online search, the COA's credibility is compromised. peptidetrust.org notes: "The lab is named. A real, findable laboratory (for example Janoshik or MZ Biolabs) - not 'tested by a US lab' with no identity you can look up."
When reviewing a claimed third-party COA, systematically check each element:
evopeak.io identifies common indicators of unreliable COAs:
peptidetrust.org reinforces: "A code or QR that opens on the laboratory's site is far stronger than a PDF hosted only by the vendor."
A COA that states only a result without method is uninterpretable. For HPLC, method details include:
For mass spectrometry, method details include:
These details allow another researcher to understand how the result was obtained and whether the methodology is appropriate for the compound analyzed.
When evaluating a peptide COA, researchers should:
A credible peptide COA is batch-specific, method-specific, and independently verifiable. It names the testing laboratory with verifiable contact information and accreditation status, includes a unique report number that can be cross-referenced on the laboratory's own system, provides both HPLC purity and MS identity results with full method details, and matches the batch number on the product vial. Systematic verification of these elements protects the integrity of research and ensures that the compounds analyzed are genuinely what the label claims.