Third-party tested peptides have a certificate of analysis — a COA — attached. That document tells you exactly what you are getting. Here is how to read one in five minutes without a chemistry degree.
Peptide Purity: What the Number Actually Means
Purity is the percentage of the sample that is the correct peptide. A COA reporting 98.5% purity means 98.5% of what was measured is the target compound. The remaining 1.5% is everything else: fragments, related compounds, leftover reagents from synthesis.
For research use, 98% or higher is the standard you want to see. Below 95% is considered low-grade material in most labs. Below 90% is a problem.
The purity number only means something if the test method is stated. Look for a line that says HPLC or RP-HPLC (reversed-phase high-performance liquid chromatography). This is a machine that separates compounds by how they move through a column — each compound moves at a predictable speed, and the machine measures how much of each thing is present. It is the industry standard for this measurement. If the COA does not name the method, the number is unverifiable.
HPLC Peptide Testing: Reading the Chromatogram
Most COAs include a chromatogram — a graph that looks like a mountain range. One large peak and several small ones is what you want.
- The large peak is the target compound. Its position on the x-axis (called retention time) should match what the lab expects for that peptide.
- Small peaks to the left or right are impurities. A well-made batch has them, but they should be visually minor.
- The area under each peak is how purity is calculated. The lab software divides the target peak area by the total area of all peaks.
If the chromatogram shows multiple large peaks of similar size, the batch contains a lot of something other than the target compound.
One thing to check: the report should state that the target peptide was used as the reference standard. A reference standard is a confirmed, pure sample the machine is calibrated against. Without it, the lab cannot say with confidence which peak is the target compound and which is something else.
What Else a COA Should Tell You
Purity is the headline number, but a complete report covers three more things.
Identity confirmation. The COA should include a mass spectrometry result — often written as MS or LCMS. Mass spectrometry checks the molecular weight of what was measured. Every peptide has a known molecular weight. If the measured weight matches, you have confirmation the material is the correct compound and not a different peptide with similar purity.
Water content. Peptides soak up water from the air during storage and handling. Water adds weight without adding active compound, so a vial that is 8% water contains less of the target peptide than you think. Look for a line called moisture content or a Karl Fischer result. Under 6% is acceptable. Some COAs skip this entirely — it is worth noting when they do.
Appearance and solubility. These are basic visual checks. The report should say something like "white to off-white powder" and confirm the material dissolved in the stated solvent. Simple, but it is a real data point.
Third Party Tested Peptides: Why the Lab’s Name Matters
Third-party testing means an independent lab ran the tests — not the manufacturer. The COA should name the testing laboratory clearly. You can then look that lab up.
A legitimate analytical lab will:
- Have a named location and contact details
- Offer services to multiple clients across different industries
- Not share a name or address with the peptide vendor
If the lab name is generic to the point of being unsearchable, or if searching it returns only the vendor’s own website, the independence of the test is questionable.
The report should also carry a date. Complex peptides are more fragile than small-molecule compounds. A COA from two years ago does not tell you the current state of the material. Look for testing within the last 12 months, and ideally within the last 6 if the product has been sitting in a warehouse.
Lot numbers matter here too. The COA lot number should match the lot number printed on your vial. A COA attached to a different batch is not evidence of anything about what you received.
A COA should state HPLC purity of 98% or above, include a mass spec identity check, name an independent lab, and carry a recent date tied to your specific lot. Those four things together give you a meaningful quality picture. If any one of them is missing, you have less information than the document appears to offer.
NXT Labs products are sold strictly as research chemicals for in vitro research, laboratory testing and analytical purposes only, and are not intended for use in any human or animal application.
NXT Labs supplies research peptides for laboratory use. Browse the full range or view current Certificates of Analysis.
