Understanding HPLC Purity Reports and COAs
What a 99% HPLC purity figure actually means, how mass spectrometry complements it, and which fields on a certificate of analysis deserve your attention.
A certificate of analysis is only useful if you can read it. Most buyers glance at the purity number and stop there, but the surrounding data tells you far more about whether a lot is fit for your study.
What HPLC actually measures
High-performance liquid chromatography separates the components of a sample and reports each as a peak. Purity is expressed as the area of the target peak relative to the total area of all peaks detected. A 99% figure means the target peptide accounts for 99% of the detected material under those specific conditions, not that the vial is 99% peptide by mass.
- Look at the chromatogram, not just the number. A clean single peak is more reassuring than a high figure with unexplained shoulders.
- Note the detection wavelength, typically 214 nm or 220 nm for peptide bonds.
- Check the gradient and column details; purity is condition-dependent.
Why mass spectrometry matters
HPLC tells you how much of one thing is present. Mass spectrometry tells you whether that thing is the peptide you ordered. The observed molecular weight on the MS report should match the theoretical weight of the sequence. A purity report without identity confirmation leaves the most important question unanswered.
Fields worth checking on every COA
- Lot or batch number, it must match the number printed on your vial.
- Test date, a COA from an unrelated lot is not evidence about your vial.
- Sequence and molecular formula.
- Observed vs. theoretical molecular weight.
- Net peptide content, where reported, which accounts for counter-ions and residual water.
- The name of the testing laboratory.
Peptide content vs. purity
These are different measurements and are frequently confused. Purity describes the proportion of peptide-related material that is your target sequence. Net peptide content describes how much of the vial's total mass is peptide at all, with the remainder being trifluoroacetate salts, water, and other residuals. Both figures are relevant when calculating concentrations.
Research products referenced in this article are for in-vitro laboratory use only.
For Laboratory & Research Use Only · Not for Human Consumption
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