What the percentage measures
A purity figure comes from reverse-phase HPLC. The instrument separates everything in the sample and reports the target compound's peak as a percentage of the total UV-absorbing material. "≥99%" means the analysis found at least 99% of that material to be the target peptide, with under 1% impurities such as truncated sequences or process residues. It is a statement about how much of the sample is the right compound — nothing more.
Why the number needs context to mean anything
A bare "99%" is marketing until three things accompany it: the method (RP-HPLC), the detection wavelength, and an acceptance threshold (the pre-defined pass/fail limit, e.g. ≥99.0%). Without a threshold, a number has nothing to be judged against. Without a method, you do not know how it was derived. A trustworthy COA states all three so the figure is verifiable rather than asserted.
Purity is not the whole picture
The most common mistake is treating purity as a single quality score. It answers one question — how much of the sample is the target — and is silent on three others: is it the right molecule (identity, by mass spec), is it biologically clean (endotoxin and sterility), and is it free of elemental residues (heavy metals). A sample can read 99% pure and still be the wrong peptide, or pure yet carry endotoxin. Purity is one line on a five-line report.
Reading the different units together
Each point on the panel uses its own scale, and a COA should not blend them into one figure:
| Result | Units | What "good" looks like |
|---|---|---|
| Purity (HPLC) | Percentage (%) | Meets or exceeds the stated threshold (e.g. ≥99.0%) |
| Identity (MS) | Da (molecular weight) | Measured mass matches theoretical mass |
| Endotoxin (LAL) | EU/mg or EU/mL | Below the stated endotoxin limit |
| Heavy metals | ppm / ppb | Each element within its limit |
| Sterility | Pass / fail | No microbial growth |
The questions a COA should let you answer
Read correctly, a Certificate of Analysis should let you confirm: the compound is the right molecule, it meets a stated purity threshold by a named method, and its contamination measures fall within defined limits — all for the specific lot in your hands, verified by an independent third-party lab rather than self-reported. If any of those is missing, the purity percentage alone should not carry the decision.
How Ethos Bio reports it
Every Ethos Bio lot is independently verified by MZ Biolabs, a third-party analytical laboratory in Arizona, on a five-point panel — RP-HPLC purity, HPLC-MS identity, endotoxin (LAL), heavy metals, and sterility — each reported against a stated threshold on the Certificate of Analysis that ships with the vial.
Read a real COA
See exactly how purity, identity, and contamination results are reported per lot in the public COA library.
Frequently asked questions
What does 99% purity mean on a peptide COA?
It means HPLC analysis found that at least 99% of the sample's UV-absorbing material is the target compound, with under 1% impurities. The figure is only meaningful when the method (RP-HPLC), the detection wavelength, and an acceptance threshold are stated alongside it.
Is a higher purity percentage always better?
Higher purity is preferable, but a percentage without an identity confirmation and contamination testing is incomplete. A sample can be 99% pure of the wrong molecule, or pure yet carry endotoxin or metals — which is why purity is read together with the rest of the panel.
What is an acceptance threshold on a COA?
An acceptance threshold is the pre-defined pass/fail limit for each test — for example ≥99.0% purity, or an endotoxin limit in EU/mg. A result is only interpretable against its threshold; a bare number with no stated limit tells you little.
How does purity relate to endotoxin and heavy-metal units?
Purity is a percentage of the organic material; endotoxin is reported in EU/mg and heavy metals in ppm or ppb. They are different scales measuring different things, so a complete COA reports each with its own units and threshold rather than reducing everything to one number.