A certificate of analysis (COA) is the lab report that travels with a batch of research peptide. It shows what was tested, what the instrument found, and whether the result passed. Knowing how to read one matters for any researcher working with these compounds.
Purity Is Not One Number
Most COAs headline a single purity figure, something like "99.2%." That number comes from a technique called HPLC — high-performance liquid chromatography — which pumps a dissolved sample through a column and measures how much of the signal belongs to the main compound versus everything else.
That number matters, but it only tells you about related impurities — meaning fragments and side-products that look similar to the target compound. It does not tell you about:
- Residual solvents left over from synthesis
- Bacterial toxins called endotoxins
- Water content
- Whether the correct molecular weight was confirmed
A complete COA shows all of these, not just HPLC purity.
For research-grade peptides, HPLC purity above 98% is a reasonable benchmark. Below 95% is a real concern. The gap between 95% and 99% is not cosmetic — those few percent represent real chemical byproducts in the vial.
Mass Spec Confirms the Right Molecule
HPLC purity tells you the sample is mostly one thing. Mass spectrometry — usually written as MS or LC-MS — confirms that the one thing is actually the compound it is supposed to be.
This matters for complex peptides with modified structures. If the MS result shows an unexpected molecular weight, you have a different compound, regardless of what the HPLC says.
A good COA will show the theoretical molecular weight alongside the observed result. They should match closely. If a COA shows HPLC purity but no mass spec result, you cannot confirm the molecule’s identity at all.
What the Other Tests Actually Mean
Water content. Peptides soak up water from the air. Too much water in a lyophilised (freeze-dried) powder affects the composition of the sample and can speed up breakdown. The Karl Fischer test measures this precisely. A result under 6% is generally acceptable for freeze-dried peptides; under 3% is better.
Residual solvents. Peptide synthesis uses organic solvents that have to be removed before the final product is dried. A COA should confirm these are below established limits. The relevant international guideline (ICH Q3C) sets limits for common solvents — for example, acetonitrile should be below 410 parts per million.
Endotoxin testing. Endotoxins are fragments of bacterial cell walls. They get into a batch through contaminated water, equipment, or raw materials. The standard test is called the LAL test — it uses horseshoe crab blood to detect contamination. Any COA for a research peptide should include an endotoxin result. The result is measured in EU/mg (endotoxin units per milligram). A result below 1 EU/mg is the standard most labs target.
Amino acid analysis. This test checks that the right building blocks are present in the right proportions. It is not on every COA but it is one of the stronger identity confirmations available, especially for complex peptides where sequencing errors during synthesis are possible.
How to Read the Lab’s Credentials
The lab that ran the tests matters as much as the numbers themselves. An ISO 17025 accreditation means the laboratory has been independently audited for technical competence. It does not guarantee perfect results, but it means the instruments are calibrated, the staff are trained, and the methods are documented.
Look for:
- The lab’s full name and location on the COA, not just a logo
- A batch or lot number that ties the report to a specific production run
- Test dates — an old COA is not current data on your vial
- The analyst’s name or signature, or at minimum a report reference number you could query
If the COA lists no lab name, or the lab name returns no verifiable address or accreditation record when you search it, the document is not independently verified.
The Short Version
A trustworthy peptide COA includes HPLC purity, a mass spec result that confirms the correct molecular weight, water content below 6%, solvent residues within ICH limits, and an endotoxin test result. The lab should be named, accredited, and traceable. Any one of those pieces missing is a gap in the picture — worth noting before you proceed with your research.
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.
Order research peptides from NXT Labs
NXT Labs supplies research peptides for laboratory research use, with third-party batch testing at a U.S.-based lab. Frequently ordered: CJC-1295 + Ipamorelin, Sermorelin, Tesamorelin and bacteriostatic water.
Browse the full range or view current Certificates of Analysis. Research use only.
