Reading HPLC purity on a peptide COA

What HPLC is doing

High-performance liquid chromatography separates components in a sample as they move through a column. On a peptide COA, the headline purity is usually the area of the main peak relative to other peaks under that method.

It is a chromatographic snapshot for one lot, on one instrument setup, on the date printed. It is not a clinical grade, a stability guarantee, or proof the material will behave the same in your assay.

Why methods are not interchangeable

Column chemistry, gradient, detection wavelength, and integration rules all change the reported number. A supplier COA and an in-house method can disagree without either being “wrong.”

When you compare vendors, compare method descriptions — not isolated percentages. How to read a peptide COA covers matching lot identifiers before you even look at the purity line.

What the purity number leaves out

Headline purity is normally an area-percent figure: the main peak as a share of the total detected peak area. It describes composition relative to what the detector saw under that method, which is not the same as the share of the vial’s weight that is peptide.

Synthetic peptides typically carry a counterion from purification — often trifluoroacetate — plus residual water and solvent. None of that registers as an impurity peak, so a vial can read 99% by HPLC while net peptide content against gross weight is materially lower. Where a COA reports peptide content separately, that is the figure to use for weighing.

Anything that does not absorb at the detection wavelength, or does not elute inside the gradient window, is also invisible to the number. Purity is a statement about a defined method, not an audit of everything in the vial.

Reading a purity claim critically

Check that the chromatogram belongs to the lot in front of you, that the method is described rather than just named, and that the detection wavelength and run time are stated. A purity figure with no method behind it cannot be compared with anything.

Treat a suspiciously round number, a missing baseline, or a chromatogram with the axes cropped as a reason to ask for the full file. How to read a peptide COA covers the surrounding document; mass spectrometry covers the identity question that purity does not answer.

How VaultLabs uses HPLC on published records

When a lot’s record is uploaded, HPLC purity may appear on that batch’s COA. Absence of an online chromatogram usually means the file is not published yet — not that the lot failed.

Your laboratory still sets acceptance criteria. VaultLabs does not interpret HPLC results for study design.