GLP1 Europe › Certificates of analysis
How to read a certificate of analysis
Short answer
A certificate of analysis is a laboratory report on a sample taken from one batch. At its best it tells you what was in that sample, on that day, by the specific tests listed.
It does not tell you what is in your vial, whether the contents are sterile, whether the powder survived shipping, or whether the document itself is real. Those four gaps are where nearly all of the risk lives, and no certificate closes any of them.
What the document is
In regulated pharmaceutical manufacturing, a certificate of analysis is one small part of a quality system that also includes audited facilities, validated processes, batch records, inspections and legal responsibility for defects. The certificate is meaningful there because of everything standing behind it.
Detached from that system, the same document is a test report from an unknown laboratory about a sample you did not see taken. It can still be informative. It just carries far less than it appears to.
What the numbers actually measure
| Field | What it measures | What it does not tell you |
|---|---|---|
| HPLC purity | The share of total detected signal belonging to the main peak, in one chromatography run | Anything the detector cannot see, and anything about weight |
| Mass spectrometry | The molecular weight of the main component, confirming it is the molecule claimed | How much of it there is |
| Peptide content | What share of the powder is actually peptide, by weight | Whether that peptide is the right one |
| Water content | Residual moisture, which affects stability | Storage conditions after leaving the laboratory |
| Appearance | Visual description of the powder | Almost nothing of consequence |
HPLC purity is narrower than it sounds
High performance liquid chromatography separates a mixture into its components and a detector measures each one as it comes off the column. The purity figure is normally the area of the main peak as a percentage of all peak area detected.
Three consequences follow, and together they are why "99 percent pure" is a smaller claim than most readers assume.
It is relative, not absolute. It describes proportions among the things that were detected. It is not a statement about the vial's total weight.
The detector has blind spots. Peptide analysis usually detects ultraviolet absorbance at a wavelength chosen for peptide bonds. Substances that do not absorb meaningfully at that wavelength, including many salts, residual solvents and water, contribute little or no peak area. They are present, they are simply not counted.
The method is a choice. Column, gradient, run length and wavelength all affect what separates and what co-elutes. Two laboratories can analyse the same powder and report different numbers without either being dishonest. This is why a certificate that states its method is worth more than one that just prints a figure.
Mass spectrometry answers a different question
Purity asks how much of the sample is the main component. Mass spectrometry asks whether that main component is the right molecule, by measuring its molecular weight against the known value.
For identity, this matters more than the purity number. A sample can be 99 percent one substance and that substance can be the wrong peptide entirely. Purity alone would look excellent. A certificate without mass spectrometry data has not established what the material is.
Peptide content is the field most people skip
Lyophilised peptide powder is not pure peptide by weight. Manufacturing leaves counterions behind, typically acetate or trifluoroacetate, and the powder holds residual water. So a vial can contain material that is 99 percent pure by HPLC while a substantial fraction of its weight is not peptide at all.
The gap is not trivial and it runs in the same direction every time: less peptide than the label weight implies. Purity and content answer two different questions and a certificate that reports only the first has left out the one that determines how much active substance is present.
The four things a certificate does not cover
Sterility and endotoxin. These are separate tests and standard peptide certificates do not include them. Endotoxin is the fragment of bacterial cell wall left behind after bacteria are killed. It survives sterilisation, it is not detected by purity testing, and it causes fever and inflammatory reactions when injected. The 2024 study discussed below found endotoxin in every sample it tested.
Your specific vial. Testing is done on a sample from a batch. Filling, capping and labelling are separate steps where a vial can be mislabelled, underfilled or swapped. The certificate describes the batch at one moment, not the object in your hand.
Everything after the laboratory. Peptides degrade with heat, light and moisture. A certificate issued at manufacture says nothing about a warehouse without climate control, a summer in a shipping container, or a parcel sitting in a hot van.
Whether the document is real. A certificate is a PDF. It can be edited, reused across unrelated batches, or produced without any testing at all. Its value depends entirely on whether the laboratory named on it exists, is independent of the seller, and can be contacted to confirm the report.
Signs a certificate is weak evidence
None of these prove anything on their own. Several together mean the document is decorative.
- No named laboratory, or a laboratory with no verifiable existence separate from the seller
- No batch or lot number, or a number that does not match the vial
- No test date, or a date that never changes across products
- No method details: no column, no gradient, no detection wavelength
- No chromatogram or spectrum, only a summary figure typed into a table
- Purity reported without peptide content
- No mass spectrometry, so identity was never confirmed
- The same certificate appearing across multiple products or batches with only the name changed
- Impossible tidiness: identical figures such as 99.9 percent repeated across every product
The distinction between third-party and in-house testing matters, but less than it is usually made to sound. Third-party only means something if the laboratory is genuinely independent, genuinely exists, and can be verified by someone other than the seller.
The honest limit
Here is the part that most pages on this subject leave out. Certificates were widely available in the grey market before anyone tested what was actually being shipped, and when researchers did test it, the results were not close.
A 2024 study in the Journal of Medical Internet Research bought semaglutide from illegal online sellers and analysed what arrived. Purity was claimed at 99 percent. Measured purity was between 7.7 and 14.37 percent. Endotoxin was present in every sample. Measured semaglutide content exceeded the labelled amount by 28.56 to 38.69 percent.
What that means for the document
A certificate is a claim, and in the grey market a claim of 99 percent purity has been measured against reality and found to be off by a factor of seven. Knowing how to read the document is useful for understanding what such a test can establish. It is not a substitute for a supply chain where someone is legally answerable if the contents are wrong.
Common questions
- Is a higher purity number always better?
Between two properly conducted tests using comparable methods, yes. Between two certificates from unknown laboratories using unstated methods, the comparison has no basis. The number without the method is not a measurement, it is a claim.
- Why do pharmaceutical products not just publish a certificate?
Because the certificate is the least of what stands behind them. An authorised medicine carries an approved manufacturing process, inspected facilities, batch release by a qualified person, stability data, a legally responsible marketing authorisation holder, and a system that collects reports when something goes wrong. The certificate is one document inside that structure rather than a replacement for it.
- Can I get a peptide tested myself?
Independent analytical laboratories exist and some accept samples from individuals. Be aware that a purity and identity test still leaves the sterility, endotoxin and stability questions open, and that testing one vial says nothing about the next one.
Sources
- Ashraf AR, Mackey TK, Vida RG, et al. "Multifactor Quality and Safety Analysis of Semaglutide Products Sold by Online Sellers Without a Prescription." Journal of Medical Internet Research, 2024;26:e65440. DOI 10.2196/65440.
- Belcourt J, Ly P, White CM. "Bypassing Prescribers and Pharmacists: Online Purchasing of Semaglutide and Tirzepatide 'For Research Purposes'." Annals of Pharmacotherapy, 2025;59(5). DOI 10.1177/10600280241277551.
- European Pharmacopoeia, general chapters on liquid chromatography and on bacterial endotoxins, for the standard methods described.
- EMA and Heads of Medicines Agencies, "Warning about sharp rise in illegal medicines sold in the EU", 3 September 2025.
This page explains what a laboratory document can and cannot establish. It is not medical advice, it is not a guide to obtaining or using any substance, and it should not be read as suggesting that any product outside the authorised supply chain can be made safe by paperwork.