Summary

Between July and September 2026, Pureline Biolabs sent one sealed vial from each of 14 batches to Janoshik Analytical, an independent laboratory in Prague, for HPLC purity analysis and mass-spectrometry identity confirmation. Three batches failed and were never listed; they are covered in the batches we rejected below. The 11 that passed were put on sale, and each of their reports also gives a measured quantity of peptide in the vial.

The purity results were tightly grouped. The quantity results were not. A supplier, or a buyer, comparing peptides on purity alone would have treated every one of these batches as essentially identical. They were not.

The Full Results

Every figure below is reproduced from the Janoshik report for that batch. Each “Verify” link opens the result on Janoshik’s own verification server, not on this site.

The two batches of retatrutide, the reta peptide, were submitted as a blind test against semaglutide, tirzepatide and retatrutide, so the laboratory identified the compound without being told what it was. The other batches were tested by HPLC with LC-MS identity confirmation. GHK-Cu is reported as separate GHK and copper figures, so we have not converted it to a single percentage of the 50mg complex.

The Three Batches We Rejected

The 11 batches above are the ones that passed. In the same round of testing, three batches did not, and none of them was ever listed for sale.

Each key can be checked on Janoshik’s verification service.

The retatrutide result is the one that matters most. Before ordering, we had checked a certificate the manufacturer had commissioned from the same laboratory, which showed a retatrutide 10mg batch at 99.397% purity and verified as genuine. The vial we sent for blind testing contained no retatrutide, semaglutide or tirzepatide at all. The certificate was genuine, but it did not describe the stock we received.

That is the reason we do not list products on the strength of a manufacturer’s certificate, however credible it looks. All three batches were quarantined and none was sold. The retatrutide UK stock now listed comes from replacement batches, and their results are the PLB-002 and PLB-003 rows in the table above.

What the Purity Figures Show

All 11 batches returned between 98.015% (KPV, PLB-011) and 99.890% (Kisspeptin-10, PLB-010), with a mean of 99.28%. On this measure alone, every batch passed our 98% listing threshold, and the spread between the best and worst result was less than two percentage points.

HPLC purity is an area-percent figure: it describes how much of the material the detector picked up was the target peptide under the laboratory’s stated method. It is a useful check for impurities and synthesis by-products. It is not a measurement of mass. Our guide to HPLC area percent versus net content explains the difference in detail.

What the Content Figures Show

The measured quantities told a different story:

• Within ±5% of label (4 batches): Ipamorelin 97.8%, KPV 98.2%, PT-141 96.5% and Selank 104.3%.
• Above label (4 batches): Semax 105.6%, Kisspeptin-10 106.0%, MOTS-c 112.3% and Retatrutide 10mg 135.1%.
• Below label (2 batches): Retatrutide 20mg 91.8% and Melanotan I 81.3%.

The clearest example is Melanotan I, batch PLB-005. Its purity of 99.805% was the third highest of the 11 batches. Its measured content of 8.13mg in a 10mg vial was the lowest relative to label. Ranked on purity, it would sit near the top. Ranked on what is in the vial, it sits at the bottom.

The two Retatrutide batches show the opposite problem. The 10mg vial measured 13.51mg, more than a third above its label, while the 20mg vial measured 18.36mg, below its label. Over-filling is not a free bonus for a researcher: it means the solution prepared from that vial is stronger than the label implies.

Why Vial Content Varies

Lyophilised peptides are normally filled as a solution and then freeze-dried, which means the amount in each vial depends on filling accuracy at very small volumes. Several other factors can open a gap between the label and the measured result:

• Gross weight versus net peptide. A lyophilised powder can contain counter-ions, such as acetate or trifluoroacetate, and residual moisture alongside the peptide itself. A vial filled to a gross powder weight will contain less net peptide than that weight.
• Filling tolerance. A few microlitres of variation in the fill volume becomes a meaningful percentage at the milligram scale.
• Measurement uncertainty. Quantitative analysis has its own margin of error, so small deviations of a few per cent should not be over-interpreted.
• One vial per batch. Each result describes the vial tested. Other vials in the same batch may differ from it.

Our article on why lyophilised peptide vials look different covers the physical side of freeze-drying and why two correctly made vials rarely look identical.

Why It Matters for Laboratory Work

Any concentration calculated for an in-vitro experiment depends on the mass of peptide that went into the solution. If a researcher reconstitutes the Melanotan I vial assuming a full 10mg, the calculated concentration will be about 23% higher than the real one. With the Retatrutide 10mg vial, it will be about 26% lower than the real one. Errors of that size can change the interpretation of a dose-response or binding experiment.

That is why our product FAQs and the reconstitution calculator encourage working from the measured content on the certificate rather than the nominal figure on the label.

How to Check Any Supplier’s Report

These checks apply to any certificate, including ours:

1. Verify it at source. Use the laboratory’s own verification link or key, not a screenshot or PDF hosted by the seller.
2. Match the batch. The batch number on the report should match the batch number printed on the vial you receive.
3. Look for quantity, not only purity. A report that gives a purity percentage without a measured mass tells you nothing about how much material is in the vial.
4. Check the test type. Identity by mass spectrometry, purity by HPLC and quantity are separate results. Sterility and endotoxin are different tests again.
5. Check the dates. The analysis date should make sense for the stock being sold.
6. Check whose vial was tested. A certificate commissioned by the manufacturer describes the sample the manufacturer sent. Only a test of a vial from the stock you are buying describes that stock.
7. Be wary of round numbers. A long run of results all reading 99%+ and exactly 10.00mg is less plausible than a set of results with normal variation.

Our guide to UK peptide supplier quality claims covers the wording to watch for on supplier websites.

Limits of This Data

This is a small data set from our own stock, tested by one laboratory, with one vial per batch. It shows how much purity and content can diverge, but it is not a survey of the wider market and does not prove how any other supplier’s products would test. None of the results address sterility, endotoxin or stability over time, and none of them constitute regulatory approval of any kind.

Common Questions

Does a 99% purity result mean a peptide vial is full strength?

No. HPLC purity describes the proportion of the detected material that is the target peptide. It does not measure how many milligrams are in the vial. In our own results, the Melanotan I batch returned 99.805% purity but 8.13mg of measured content in a 10mg vial.

Why would a vial contain more peptide than its label states?

Common reasons include filling tolerances at milligram scale, the difference between gross powder weight and net peptide content, and the measurement uncertainty of the quantity method. Our Retatrutide 10mg batch PLB-003 measured 13.51mg.

Can a manufacturer’s own certificate of analysis be trusted?

It can be genuine and still not describe your stock. In our testing, a manufacturer’s own certificate showed a retatrutide batch at 99.397%, but the vial we received and sent for blind testing contained no retatrutide. Independent testing of a vial from the actual stock is the only way to confirm what it contains.

How can I verify a Janoshik certificate myself?

Every Janoshik report carries a unique key. Open the verification link or enter the key at verify.janoshik.com and check that the compound, batch details, purity and quantity match the certificate the supplier shows you.

Does a certificate of analysis prove a peptide is sterile?

No. A standard HPLC and mass spectrometry certificate addresses identity, purity and, where requested, quantity. Sterility and endotoxin are separate tests, and none of the results in this article cover them.

Should laboratory concentrations be calculated from the label or the measured content?

From the measured content where a quantity result is available. Calculating from the label would misstate the solution concentration by the same percentage the vial is over or under its stated mass.

Sources

1. Janoshik Analytical test reports #209938–#209947, analysed 29 July 2026, and #226521–#226522, analysed 2 September 2026. Individual verification links are given in the results table above.
2. Janoshik Analytical test reports for the three rejected batches, verify keys 97L4JC88LRJ8 (retatrutide), FNJI8AQD41LA (tesamorelin) and L34Q99DU72D8 (TB-500), analysed July 2026.
3. Pureline Biolabs. Independent peptide lab reports, including the full certificate images for each batch.
4. Janoshik Analytical. janoshik.com.

Published by Pureline Biolabs Ltd, a UK-registered supplier of laboratory research materials, company number 17236739. Data correct as of October 2026. Factual corrections are welcome through the contact page.