What Peptide Purity % Means (and What It Does Not)

“98% pure” is the most quoted figure in the research peptide market and the least understood. It is a precise measurement of one specific thing — and silent about several others. Knowing the difference is what separates an informed reading of a COA from a marketing impression.

What the number is

Purity comes from HPLC. The instrument separates the sample into peaks and reports the area of the target peak as a percentage of the total detected peak area. So 98% purity means the target accounts for roughly 98% of what the detector saw, with the other 2% being related impurities — truncated chains, oxidized variants, or deletion sequences from synthesis.

What it does not tell you

The purity percentage is narrow by design. On its own it does not tell you:

• Identity — whether the main peak is even the right molecule. That requires mass spectrometry.
• Net peptide content — how much actual peptide is in the powder by mass.
• Contaminants — endotoxin, heavy metals, and residual solvents are separate screens. See contaminant testing.
• Anything outside the detection window — components the method does not detect do not appear in the percentage.

Purity vs net peptide content

This distinction matters whenever mass is being considered, because water and counter-ions add weight without adding peptide. A COA that reports both purity and net content is giving you a fuller picture than purity alone.

Reading thresholds

Many labs treat 98% as a pass threshold and 99%+ as high grade, but these are conventions. A threshold is only meaningful when the identity is confirmed and the contaminant screens are clean.

Putting it in context

Read purity as one of three legs: identity, purity, and contaminants. Drop any leg and the stool falls over. The companion guides on reading a COA and HPLC vs mass spec show how the legs fit together. On Peptuvia, purity from independent labs is published per batch on the verification page rather than quoted as a single marketing figure.