What HPLC Purity Actually Means on a Peptide COA

HPLC purity tells you what share of the material the lab detected is the named peptide. A result of 99.5% means that, of everything the instrument picked up, about 99.5% was the compound on the label and about 0.5% was something else, usually closely related peptide fragments left over from synthesis.

It does not tell you how many milligrams are in the vial. That is a separate line on the report, usually called content or net content.

High-performance liquid chromatography pushes a dissolved sample through a packed column. Different molecules travel through it at different speeds, so they come out at different times, and a detector records each one as a peak on a chart.

Purity is calculated from the size of the main peak compared with all the peaks together. That is why it is often described as area percent.

Identity. HPLC shows that one main thing is present, not what that thing is. Confirming identity needs a second method, most often mass spectrometry, or a comparison against a known reference standard.

Content. A vial can be 99% pure and still hold less than its label. Purity describes the quality of what is there; content describes the amount.

Everything else in the powder. Lyophilized peptides also contain some water and counter-ions (salts such as acetate) left from manufacturing. These usually do not show up as impurity peaks, which is another reason purity and content are reported separately.

Read purity and content together. A good report shows high purity and a measured content at or above the label.

Compare like with like. Purity from one lab and one method is not always directly comparable with a figure from another, so a named lab and a stated method matter more than a decimal place.

Every product we sell with a published report shows both numbers on its page.