One skill separates an informed peptide researcher from one flying blind: reading a certificate of analysis (COA) before ordering. A COA is the document a lab produces after testing a batch. It tells you what is actually in the vial, not just what the label claims. The two numbers that matter most are purity from HPLC testing and the peptide mass confirmed by mass spectrometry.
Peptide Purity Testing: What the Numbers Actually Mean
Purity is the percentage of your sample that is the correct peptide. Everything else — broken fragments, leftover chemicals from synthesis, water — makes up the rest.
For research-grade peptides, 98% purity or higher is the standard to look for. Some suppliers list 95% as acceptable. That 5% gap is not empty space — it is unknown material in your vial.
HPLC purity and mass spec identity are two different measurements. Purity tells you how much of the peptide is there. Mass spec confirms which peptide it is. You need both numbers on the same COA.
A COA without a mass spec result tells you the batch is mostly pure — but does not confirm what peptide you actually have.
HPLC Peptide Testing: Reading the Chromatogram
HPLC stands for high-performance liquid chromatography. The machine pushes your sample through a column and records when different molecules come out the other end. The output is a graph with peaks — each peak is a different compound.
The main peak is your peptide. Smaller peaks beside it are impurities.
What to look for on an HPLC report:
- A single tall, clean main peak
- Purity reported as area percent — this is what the main peak represents as a share of all peaks combined
- Retention time listed (the point on the timeline where the main peak appears) — this should match the lab’s reference standard for the peptide in question
- Any impurity peaks named or quantified, not just lumped into a single "other" number
What raises concern:
- Multiple peaks of similar height — this suggests the batch contains significant byproducts
- Purity listed as a weight percentage without a chromatogram attached — this is not standard HPLC reporting
- A chromatogram image that is blurry or oddly cropped — you cannot verify a partial graph
The HPLC report should show you the actual graph, not just a typed number. If there is no graph, there is no way to verify the claim.
Peptide COA Testing: What Else the Document Should Contain
A complete COA for a research peptide covers more than purity. Here is what a thorough document includes:
| Test | What it confirms | Acceptable result |
|---|---|---|
| HPLC purity | Correct peptide as % of sample | ≥ 98% |
| Mass spectrometry | Molecular weight matches the stated peptide | Within 1 Da of theoretical |
| Water content | How much moisture is in the lyophilised powder | Typically < 8% |
| Residual solvents | Leftover synthesis chemicals | Below standard safety limits |
| Appearance | Visual check of the powder | White to off-white powder |
The batch number on the COA should match the batch number printed on the vial or packaging. If those do not match, the COA belongs to a different batch.
Date matters too. A COA from several years ago tells you nothing about today’s stock.
Third-Party Tested Peptides: Why the Lab Name Matters
Third-party tested means the testing was done by a lab with no financial connection to the seller. This is the standard to look for. An in-house test, done by the manufacturer testing their own product, is not independent.
Reputable independent labs used for peptide testing include names like Intertek and university-affiliated analytical labs. The COA should name the testing lab clearly and ideally include a report number you can use to query the lab directly.
Geographic location of the lab matters for one reason: a lab operating under US or EU accreditation — ISO/IEC 17025 is the relevant standard, meaning the lab’s methods have been independently verified — is accountable in a way that an unnamed offshore lab is not.
If the COA lists no lab name, or lists a lab you cannot find with a basic web search, the document is unverifiable.
Practical Summary
Read every COA before you commit to a batch. The minimum you need is an HPLC purity of 98% or above, a mass spec result confirming the peptide’s molecular weight, and a named third-party lab. Cross-check the batch number on the COA against the batch number on the product. If any of those three things are missing, you do not have enough information to assess what you are buying — regardless of what the product page says.
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.
