Peptide testing is the laboratory analysis of one lot of a peptide to establish what it is, how pure it is, how much of it is in the vial, and whether it carries contaminants. A certificate of analysis (COA) reports those results for the sample the lab received. This guide explains each test, what it can and cannot show, and how to check a certificate with the laboratory that issued it.
The tests on a peptide certificate
| Test | What it answers | How it is usually reported | What it does not tell you |
|---|---|---|---|
| HPLC purity | What share of the material that the detector sees is the target peptide |
Peak-area percentage, e.g. 99.62% |
Not the amount of peptide in the vial, and not contaminants the method cannot detect |
| Identity | Is it the right molecule? |
Confirmed / not confirmed, by HPLC retention time against a reference standard, or by mass spectrometry |
Not purity or quantity |
| Net peptide content (or quantity) | How many milligrams of peptide are actually present |
mg per vial, or mg/mL for a solution, against the label |
Not whether that peptide is pure |
| Endotoxin | Bacterial endotoxin load |
EU/mL by LAL assay (USP <85>), sometimes against a limit |
Not whether live bacteria are present |
| Sterility | Microbial growth |
No growth / growth, by PCR or culture |
Not endotoxin |
| Heavy metals | Arsenic, cadmium, lead, mercury, chromium |
Per-metal result by ICP-MS against limits |
Not organic impurities |
| Fentanyl screen | Contamination with fentanyl |
Detected / not detected by immunoassay, with its cutoff |
Not other drugs |
Our guide to reading a peptide COA goes through each of these lines on a real certificate.
Purity and content are different numbers
This is the most common misunderstanding. HPLC purity says what fraction of the detected material is the target peptide. It says nothing about how much peptide is in the vial, because a lyophilised peptide also contains counter-ions (such as acetate) and water. Net peptide content is a separate measurement, and it is the one that tells you whether a “10 mg” vial holds 10 mg.
A real example from our catalogue: the current 10 mg lot of GLP-3 Reta (retatrutide) measured 99.90% HPLC purity and 10.72 mg net peptide content. A vial can score high on one and low on the other, so a certificate that reports only purity is reporting half of the answer.
Identity: retention time vs mass spectrometry
Identity can be shown in two main ways. HPLC retention time compares when the sample elutes with when an authentic reference standard of the same peptide elutes under the same conditions; a match supports identity. Mass spectrometry measures the molecular mass directly and can distinguish peptides that elute close together. The ILS Laboratories certificates on our product pages confirm identity by HPLC retention-time match to a reference standard; the HYTE Research Division certificates use HPLC with diode-array detection (HPLC-DAD). Each product page states which.
Peptide testing labs and ISO/IEC 17025
ISO/IEC 17025 is the international standard for the competence of testing and calibration laboratories. Accreditation is granted for a defined scope of methods, so the useful question is whether the tests on your certificate are within that scope, not just whether the lab “is accredited”.
Most of our current certificates come from ILS Laboratories in San Diego, which states ISO/IEC 17025 accreditation for activities within its published scope. Others come from HYTE Research Division and Accurate Test Labs. Every certificate on file today, by laboratory:
| Laboratory | Sizes on sale | Products | HPLC purity reported | Analysed |
|---|---|---|---|---|
| ILS Laboratories | 24 | 16 | 99.26% – 99.90% | 3 Sep 2026 – 21 Sep 2026 |
| HYTE Research Division | 8 | 8 | 99.74% – 99.97% | 15 Apr 2026 – 7 Oct 2026 |
| Accurate Test Labs | 4 | 3 | 99.32% – 99.80% | 22 Jul 2026 – 24 Aug 2026 |
| Laboratory not named | 1 | 1 | 99.62% | 1 Jul 2026 |
37 sizes on sale today carry a certificate. Counted from the certificate data on each product page when this page loads.
How to check a certificate with the lab
A certificate is only as good as your ability to confirm it came from the lab. ILS Laboratories prints a QR code and an access code on each certificate; entering the code at portal.ils-lab.com/verify shows the lab’s own record of that report, including the client, product, size, lot and analysis date. For any lab, check that:
- the lot number on the certificate matches the lot on your vial or order;
- the size and product name match what you bought;
- the analysis date is recent enough to be the current lot;
- the lab’s own record, where it offers one, shows the same results.
One limit to keep in mind: the product name, lot number and label claim on a certificate are supplied by the client who sent the sample. The lab reports what it found in that sample; it does not independently confirm that the sample came from the lot named.
Independent testing databases
Some organisations buy peptide samples on the open market and test them themselves, then publish the results by vendor. Finnrick is one example; others collect and index vendors’ own certificates. Results from samples bought independently are useful because they test what is actually shipped, not what a vendor chose to send. Our longer guide to third-party tested peptides covers what to look for.
What peptide testing cannot do
- It describes the sample tested, at the time it was tested. Storage and handling after that are not covered.
- A test only finds what it is designed to find. A clean HPLC trace says nothing about endotoxin, and a negative fentanyl screen says nothing about other substances.
- For a blend, a single total figure hides the ratio. Look for each component quantified separately, as on our KLOW and BPC-157 / TB-500 blend certificates.
