HPLC vs Mass Spectrometry on a Peptide COA: What Each Test Actually Tells You
A certificate of analysis (COA) for a research peptide usually lists two tests: HPLC and mass spectrometry. They answer different questions, and a COA with only one of them leaves a gap. This guide explains what each method measures so you can read a COA critically. All products discussed on this site are sold for laboratory research use only.
What HPLC measures: purity
High-performance liquid chromatography separates the components of a sample as it passes through a column. A detector, commonly UV absorbance near 214 nm for peptides, records a peak for each component. Purity is typically reported as the area of the main peak divided by the total peak area. A figure such as “99%” therefore means the main peak accounts for that share of detected absorbance, not that the sample is 99% of a specific labeled mass.
HPLC does not by itself prove that the main peak is the intended peptide. A different compound can elute as a clean single peak.
What mass spectrometry measures: identity
Mass spectrometry measures the mass-to-charge ratio of ions from the sample. For a peptide, the observed molecular weight should match the theoretical value for the labeled sequence within instrument tolerance. This is the identity check. It confirms the right molecule is present, but it does not quantify how much of the sample it makes up.
Why you need both
HPLC without mass spectrometry says the sample is mostly one thing but not what. Mass spectrometry without HPLC says the right molecule is present but not how much impurity surrounds it. Together they cover identity and purity.
What neither test tells you
- Net peptide content: the actual peptide mass versus water, counter-ions and salts in the vial.
- Endotoxin and sterility: separate assays.
- Residual solvents or heavy metals: separate assays.
Checklist for reading a COA
- Does it name the lab, the batch or lot number, and a test date?
- Does the batch number match the vial you received?
- Are both an HPLC chromatogram and a mass spectrum included, not just a summary line?
- Does the observed mass match the theoretical mass for the stated peptide?
- Is the report from an independent lab, and can you verify it with that lab?
For more detail, see our guides on how to read a COA and catch a fake one, what peptide purity really tells you and lab testing information, or browse the research peptide catalog. For laboratory research use only; not for human or veterinary use.
