HPLC Purity Testing for Research Peptides
Reversed-phase HPLC is the standard purity method for synthetic peptides. Understanding how the number is produced makes it much harder for a supplier to sell you a meaningless one.
Updated August 8, 2026
How the separation works
The sample is injected onto a hydrophobic stationary phase, typically C18, and eluted with an increasing gradient of organic solvent against an aqueous phase containing an ion-pairing agent. More hydrophobic species retain longer. A UV detector, usually at 214 nm where the peptide bond absorbs, records what comes off the column and when.
Why the method matters as much as the result
The same material can report different purity under different gradients. A shallow gradient resolves closely-related impurities that a steep one hides under the main peak. That is why a defensible COA states the column, gradient, flow rate, detection wavelength, and run time — the conditions are part of the claim.
- Column chemistry and dimensions
- Mobile phase composition and ion-pairing agent
- Gradient profile and total run time
- Detection wavelength
- Injection volume and sample concentration
Impurity classes you will see
Deletion and truncation sequences
Incomplete coupling during solid-phase synthesis leaves chains missing one or more residues. These typically elute close to the target peak because they are structurally similar.
Oxidation products
Methionine, cysteine, and tryptophan residues oxidize readily. Oxidized species usually elute earlier than the parent peptide because they are more polar.
Aggregates and dimers
Sequences prone to self-association can show late-eluting or broadened features. Persistent aggregation across lots is a formulation and handling question, not just an analytical one.
Reading the trace critically
- Is the main peak symmetric, or does it tail into a shoulder?
- Is the baseline flat, or drifting enough to distort integration?
- Are impurity peaks labeled with retention times and areas?
- Does the reported percentage match the areas shown?
What we publish
Every lot is assayed by an independent laboratory and the full chromatogram is retained with the batch record, not summarized into a single figure on a product page.
All compounds are sold strictly for laboratory research and development. They are not for human or veterinary use, and nothing on this page is medical advice.
Frequently asked questions
- What purity is typical for a research peptide?
- Most well-synthesized research peptides report above 98% by reversed-phase HPLC, but the figure is only meaningful alongside the method conditions and the chromatogram it came from.
- Why is 214 nm used for detection?
- The peptide bond absorbs strongly near 214 nm, so detection at that wavelength responds to the backbone itself rather than only to aromatic side chains.
- Can HPLC detect the wrong compound entirely?
- Not on its own. A pure but incorrect compound can still produce a single sharp peak. Mass spectrometry is what establishes identity.
