Every research peptide supplier quotes a purity figure. Very few publish the method that produced it, and the gap between those two groups is the most efficient filter a buyer has. These are the questions worth asking, and what the answers tell you.
1. At what wavelength was the analysis run?
The expected answer is 214 nm, where the peptide backbone amide absorbs and essentially every peptide-derived species is visible. A figure measured only at 280 nm reflects aromatic residues alone and can look considerably cleaner than the material is, particularly for sequences with no tryptophan or tyrosine. A supplier who does not know the wavelength did not run the analysis.
2. What was the gradient?
Gradient slope changes the number more than almost anything else. A shallow gradient over a longer run resolves near-eluting impurities — deletion sequences, oxidation products — and subtracts them from the main peak. A steep gradient merges them in and returns a higher figure from identical material. “5 to 65% acetonitrile over 30 minutes” is an answer; “a standard gradient” is not.
3. Which column?
Stationary phase, particle size and pore size all affect resolution. This is not a trick question; it is a check that a real instrument was involved.
4. Who performed the analysis?
In-house or independent. Both can be done well, but an independent laboratory has no commercial interest in the result, and that difference is exactly what a purchaser is trying to buy. Ask for the laboratory to be named.
5. When was it performed, and on what material?
An analysis has a subject. If the trace was run on material that is not what would ship to you, the document is a sample of the supplier’s history rather than evidence about your vial. This is where most suppliers become vague, and it is worth pressing.
6. Can I see the chromatogram, not just the number?
The trace shows baseline quality, peak symmetry and shoulders on the main peak — everything a summary figure discards. A supplier willing to publish the image is making a much stronger claim than one willing to publish only a percentage.
7. Is identity confirmed separately?
Chromatographic purity and identity confirmation are different questions. Retention time is consistent with an identity; it does not establish one. If a supplier offers a single number as evidence of both, they have not understood what they are selling.
8. What is the net peptide content, and the counter-ion?
Purity is a peak-area ratio. Net peptide content is a mass fraction. A supplier who conflates them is either not measuring the second or not reporting it, and a purchaser relying on the first to calculate molarity will overestimate concentration.
What good answers look like in practice
A supplier who can answer all eight quickly has an analytical process. One who answers three and deflects the rest may still be selling good material, but you are buying on trust rather than on evidence, and you should price that difference into the decision.
Our position is to publish the independent reverse-phase HPLC analysis for each product on its product page, readable before an order rather than promised after one, and to state plainly what we do not issue: our vials carry no batch or lot number, and a vial is matched to its published test by crimp and cap colour.
Research use only. All products supplied by Battle Born Peptides are laboratory reference materials for in-vitro research and analytical use by qualified professionals. They are not drugs, foods, dietary supplements, cosmetics or medical devices; they are not approved by the FDA or any other regulator for use in humans or animals; and they are not intended to diagnose, treat, cure, mitigate or prevent any disease, or to affect the structure or any function of the body of humans or animals. Nothing in this article is preparation, handling or dosing guidance. See our full research-use terms.