A certificate of analysis is the only document in this industry that is supposed to be boring. It reports what a laboratory measured on one batch of material. When it is written properly it answers four separate questions, and when it is written badly it answers one question and implies the other three.
This guide walks a research peptide COA from top to bottom. The examples use PUŪRA's own certificate layout, but the logic applies to any supplier's.
The header: who, what, when
Before any result, a certificate should state the product name, the lot or batch number, the date the analysis was performed, and the name of the laboratory that performed it. All four.
The lot number ties the certificate to a physical batch. The date establishes that the analysis is current. The laboratory name is what turns "third-party tested" from a slogan into a checkable claim. If any of these is missing, the rest of the document is unmoored. A purity figure with no lot number is a purity figure for something.
Line one: identity
Method: LC-MS (liquid chromatography, mass spectrometry).
Identity answers the first question: is this the molecule it claims to be? The instrument measures the mass of the compound and the certificate reports it against the theoretical molecular weight calculated from the amino acid sequence. A match confirms that the sequence ordered is the sequence in the vial.
What to look for: an observed mass and a theoretical mass, both stated, within the instrument's tolerance of each other. A certificate that says "Identity: Pass" with no numbers is asking for trust rather than offering evidence.
What identity does not tell anyone: how much of the sample is that molecule. A vial can pass identity and still be mostly something else.
Line two: purity
Method: RP-HPLC (reversed-phase high-performance liquid chromatography), UV detection.
Purity answers the second question: of the peptide material present, what fraction is the target sequence rather than a related impurity? The instrument separates the sample into its components and reports the target as a percentage of the total detected area. Common impurities in synthetic peptides are deletion sequences, where one residue failed to couple during synthesis, and oxidized or deamidated variants of the correct sequence.
What to look for: a specific figure, such as 98.7%, and ideally the chromatogram itself. Real batches vary. PUŪRA's specification is 98% or higher, and the published range across current lots runs from 98.3% to 99.8%. A supplier whose every lot reads exactly 99.0% is publishing a target, not a measurement.
What purity does not tell anyone: how much peptide is in the vial by weight. This is the single most common confusion on a COA, and the next line is where it gets resolved.
Line three: net peptide content
Method: gravimetric, or amino acid analysis.
Lyophilized powder is not pure peptide. It contains counterions carried over from purification, most often acetate or trifluoroacetate, and residual water. Net peptide content reports the fraction of the powder that is actually peptide by mass. For research-grade material this commonly falls between 70% and 90%.
Purity and net peptide content are independent. A sample can be 99% pure and 78% peptide by mass, and both figures are correct. Purity describes the peptide. Net content describes the powder. A researcher weighing out material needs the second number, and most certificates in this industry do not show it.
What to look for: a percentage, reported per lot. Its absence is not proof of a problem, but its presence is a strong signal that the supplier understands what a researcher needs from the document.
Line four: contamination
Methods: LAL for bacterial endotoxin; elemental analysis for heavy metals.
Contamination answers the fourth question: what else is in here that should not be? Bacterial endotoxin is measured by the limulus amebocyte lysate assay and reported in endotoxin units per milligram. Heavy metals screening reports lead, arsenic, cadmium and mercury against defined limits.
What to look for: numbers against a stated limit. A figure such as 0.4 EU/mg set against a stated limit is a result. "Endotoxin: Pass" is a summary of a result someone chose not to show.
What these lines must not become: a statement of what the material is ready for. Endotoxin and heavy-metals results describe the quality of research material. Any certificate or product page that reads these results as clearance for a particular use has stepped outside what a research-use-only supplier can say, and outside what the assay measures.
The footer: specification and release
A complete certificate ends with each result set against its acceptance criterion, an overall pass or fail, and a signatory. The word that matters is rejected. A supplier with a real release standard has lots that fail it, and those lots do not ship. If a supplier's certificates have never once shown an out-of-spec result across years of batches, either the chemistry is perfect or the certificates are.
Six red flags, in order of how fast they can be spotted
- No lot number. The certificate belongs to nothing in particular.
- No laboratory name. The seller tested the seller's product.
- The same PDF on every product page. One certificate cannot describe six molecules.
- Round numbers everywhere. 99% on every lot is a house style, not a chromatogram.
- "Pass" with no figures. A result was measured and then hidden.
- A test date that predates the restock. The certificate is for a batch that has already sold out.
Where PUŪRA's certificates live
Every listed product carries the certificate for the lot currently shipping, with the laboratory named and the test date shown. The four analyses run on every lot, identity, purity, net peptide content and elemental screening, are described with their methods on the Process page. If a lot's certificate is not yet back from the laboratory, the product card says so rather than showing another lot's.
Frequently asked questions
What should a peptide certificate of analysis include? Product name, lot number, test date, the name of the laboratory that ran the analysis, an identity result by mass spectrometry, a purity figure by HPLC, net peptide content, contamination results such as endotoxin and heavy metals, and each result set against its acceptance criterion.
What is the difference between purity and net peptide content? Purity is the fraction of the peptide material that is the target sequence rather than a related impurity. Net peptide content is the fraction of the powder in the vial that is peptide at all, after counterions and water. A sample can be 99% pure and 78% peptide by mass, and both numbers are correct.
How do I verify a peptide COA is real? Check that the lot number on the certificate matches the vial, that the laboratory named on it exists and can be contacted, that the test date is recent and later than the synthesis date, and that results are figures against limits rather than the word "Pass."
What is a normal endotoxin level on a peptide COA? Endotoxin is reported in endotoxin units per milligram against a limit the laboratory states. The figure describes the bacterial load of research material. It is a quality metric, not a statement about what the material is ready for.