How to Read a Peptide Certificate of Analysis
A certificate of analysis is a testing record, not a quality guarantee. Here is what each section actually reports and which questions it leaves open.
Key takeaways
- 1.A certificate of analysis documents specific tests on a specific sampled lot, not overall product quality.
- 2.Chromatographic purity is a relative area measurement and can miss anything the detector or method does not see.
- 3.Identity, purity, and net peptide content are three separate questions answered by three different methods.
What a certificate of analysis is
A certificate of analysis (CoA) is a document issued by a laboratory that records the results of specific tests performed on a specific sample. It is a record of measurement, not a general statement of quality. A CoA can only speak to the material that was tested, using the methods listed, on the date shown.
The header block
The top of a CoA identifies the material and the sample. Look for the product or compound name, a lot or batch identifier, the sample receipt date, the analysis date, and the issuing laboratory. If a lot number on the CoA does not match the lot number on the container in front of you, the document does not describe your material.
Methods listed
Each reported result should name the analytical method used. Purity by reversed-phase HPLC, identity by mass spectrometry, water content by Karl Fischer titration, and counterion content by ion chromatography are common entries. A result with no stated method cannot be interpreted, because the number has no context for how it was produced.
Purity and how it is expressed
Purity on most peptide CoAs is chromatographic purity: the area of the main peak divided by the total area of all detected peaks, usually at a stated UV wavelength. This is a relative measure. Substances that do not absorb at that wavelength, or that do not elute under the chromatographic conditions used, are invisible to the measurement.
Identity confirmation
Mass spectrometry results typically list a theoretical monoisotopic or average mass and an observed mass. Close agreement supports the conclusion that the molecule has the expected molecular weight. It does not by itself resolve sequence ordering or stereochemistry.
Net peptide content
Net peptide content describes how much of the weighed powder is actually peptide, with the remainder being water, counterions such as trifluoroacetate or acetate, and residual salts. A vial can report high chromatographic purity and still be a minority peptide by mass. Amino acid analysis or nitrogen determination is the usual method here.
Dates, signatures, and traceability
A CoA should carry an issue date and an identified signatory or authorising analyst. Traceability matters: an unsigned PDF with no laboratory address, no method references, and no lot linkage is an assertion rather than a record.
Reading the chromatogram, not just the number
Where the raw chromatogram is attached, examine peak shape and the baseline. A single sharp main peak with a flat baseline supports the stated purity figure. A broad main peak, a shoulder, or an unresolved cluster near the main peak can inflate an area-percentage result.
What a CoA does not tell you
A CoA does not establish sterility, endotoxin level, or biological activity unless those tests are explicitly listed. It does not establish stability over time, and it does not speak to how the material was handled after the sample was drawn.
Related reading
Limitations
This article describes how CoA documents are structured and reported. It is not a validation protocol, and it cannot verify the accuracy or authenticity of any individual document. Laboratory practice varies, and the presence of a CoA does not itself demonstrate that a laboratory is accredited or that its results are reproducible.
Sources
- 1.USP General Chapter <621> Chromatography (USP–NF, subscription access)
- 2.ICH Q2(R2) Validation of Analytical Procedures (2023)
- 3.ISO/IEC 17025:2017 General requirements for the competence of testing and calibration laboratories
Research worth reading. Updates worth sharing.
Get clear explanations of metabolic health, healthy aging, and emerging research, plus occasional updates from our affiliated research business, TPG Bioscience.
Educational information only. This article does not provide medical advice, diagnosis, dosing, or treatment recommendations.
Related articles
Purity, Identity, and Content: What Different Tests Measure
Three words that are often used interchangeably describe three genuinely different measurements. Confusing them is the most common misreading of peptide test data.
Recomp Report Editorial Team · 6 September 2026
Endotoxin Testing and Sterility Testing: Different Questions
Sterility and endotoxin content are not the same attribute, and passing one test says very little about the other.
Recomp Report Editorial Team · 25 August 2026
HPLC and Mass Spectrometry: What Each Method Can Tell You
Separation and mass measurement answer complementary questions. Neither one alone characterises a peptide sample.
Recomp Report Editorial Team · 31 August 2026