If you have ever opened a Certificate of Analysis from a research-peptide supplier, you have seen a number that looks something like “Purity by HPLC: 98.4%”. That figure decides whether your downstream experiment is interpretable or contaminated by unknowns. This article explains what HPLC actually measures, what the percentage means in practice, and what to look for on a Certificate.
What HPLC measures, in plain terms
High-Performance Liquid Chromatography (HPLC) is an analytical technique that pushes a dissolved sample through a column packed with a stationary phase under high pressure. Different molecules travel through the column at different speeds based on their physical and chemical properties, separating into peaks that are recorded by a detector — usually a UV-absorbance detector at a wavelength like 214 nm or 220 nm.
For a peptide, the result is a chromatogram with one large peak (your target peptide) and, ideally, very small or absent peaks for everything else. The purity percentage reported on a Certificate is the area of the target peak divided by the total area of all peaks, expressed as a percent.
What “98% purity” actually tells you
A purity figure of 98% by HPLC means that 98% of the UV-absorbing material on the chromatogram belongs to your target peptide. The remaining 2% is some combination of:
- Truncated sequences — peptide chains that failed to fully assemble during solid-phase synthesis
- Deletion sequences — chains missing an internal amino acid
- Oxidation products — common with methionine, cysteine, and tryptophan residues
- Residual scavengers or coupling reagents from synthesis
For most pre-clinical research applications, ≥95% HPLC purity is considered acceptable; ≥98% is preferred for quantitative or receptor-binding work where small contaminants can produce misleading signals.
HPLC versus mass spectrometry — they are not the same
HPLC answers the question “how much of the sample is the target?”. Mass spectrometry (MS) answers a different question: “does the target have the expected mass?”. A reputable Certificate of Analysis reports both. HPLC gives you purity; MS confirms identity. Either alone is incomplete.
Why batch-by-batch testing matters
Peptide synthesis is sensitive to dozens of variables — resin loading, deprotection efficiency, coupling time, cleavage cocktail composition. Two batches of the same sequence from the same lab can differ in purity. This is why we issue a Certificate of Analysis for every batch we supply, not a single Certificate for an entire production run.
What to verify on the Certificate
When you receive a peptide for research, take a minute to check that the Certificate includes:
- The peptide name and sequence
- The batch or lot number — this must match the vial label
- HPLC purity percentage and the wavelength used for detection
- Observed mass (from MS) and theoretical mass for comparison
- The date of analysis and the testing laboratory
If any of these are missing, ask the supplier. Anyone selling research peptides without batch-specific HPLC and MS data is asking you to trust without verifying — and that trust is incompatible with reproducible science.
Further reading
For our full policy on quality control, see the FAQ, the Disclaimer, and any of our individual product pages where the typical purity range is published. Every product we offer at Ouro Peptides ships with batch-specific third-party HPLC and MS documentation.
For in-vitro research use only. Not for human or veterinary consumption.