A purity figure on a certificate of analysis is often treated as a single number. In practice it is the result of a specific method, with a specific detection wavelength, a specific integration rule and a specific chromatographic system. Understanding that context is what separates a usable COA from a marketing claim.
What RP-HPLC purity actually measures
Reversed-phase high-performance liquid chromatography (RP-HPLC) separates a peptide sample by hydrophobicity. The peptide of interest elutes as a main peak; closely related impurities — deletion sequences, truncated chains, oxidation products and residual protecting-group species — elute nearby. Detection is commonly performed by UV absorbance at 214 nm, where the peptide bond absorbs strongly.
Purity is then reported as the area of the main peak divided by the total integrated peak area, expressed as a percentage. This is an area-normalisation result, not an absolute mass fraction. Two consequences follow: impurities that do not absorb at 214 nm can be under-represented, and a co-eluting impurity can be folded into the main peak. That is why a purity grade should always be read together with the method and the raw chromatogram.
Why mass spectrometry answers a different question
HPLC tells you how much of the detected material behaves like the main component. It does not prove that the main component is the intended molecule. Electrospray ionisation mass spectrometry (ESI-MS) supplies the molecular weight, and therefore identity confirmation against the expected sequence. A batch can show a clean 99% chromatogram and still be the wrong compound.
For research-grade supply these two assays are complementary, not interchangeable. Where structural ambiguity remains — for example with cyclic, disulfide-paired or heavily modified sequences — NMR or amino acid composition analysis can be added on request.
A typical verification workflow
| Step | Assay | Question answered | Typical turnaround |
|---|---|---|---|
| 1 | RP-HPLC, UV 214 nm | How much of the sample is the main peak? | 2–5 business days |
| 2 | ESI-MS / LC-MS | Is the main peak the expected molecular weight? | 3–5 business days |
| 3 | Karl Fischer titration | How much residual water is present? | 1–2 business days |
| 4 | Amino acid composition | Does the composition match the sequence? | 5–10 business days |
| 5 | Endotoxin (LAL) / sterility | Does the batch meet the protocol's limits? | 3–14 business days |
What to ask your supplier for
- A batch-linked COA that names the method, column and detection wavelength.
- The raw HPLC chromatogram, not only the processed percentage.
- The MS spectrum with the observed and theoretical molecular weight.
- A statement of the integration rule and how related impurities were handled.
- MSDS and documented storage conditions for the supplied form.
At Helios Bio Labs, every report includes the method, the raw chromatogram or spectrum, and a pass/fail conclusion. Testing is performed under an ISO/IEC 17025 (CNAS, ILAC-MRA) and CMA aligned quality system, with 20 mg of lyophilized powder or 1 mL of solution required per test.
All peptide products are supplied for research use only. They are not for human or veterinary use, and are not intended for therapeutic, diagnostic, cosmetic or injection applications.
Common questions
Are Helios Bio Labs peptides supplied for research use only?
Yes. Every peptide is supplied for research use only. It is not for human or veterinary use, and not for therapeutic, diagnostic, cosmetic or injection application.
Which documents accompany a batch?
A batch-linked certificate of analysis stating method, result, specification and a pass/fail conclusion, together with the raw HPLC trace and the MS spectrum. MSDS and a packing list travel with the shipment.
Can additional analytical testing be commissioned?
Yes. Testing can be commissioned for a specific batch. Send the method, the specification and the sample quantity through the inquiry form and the team will confirm feasibility and turnaround.
Keywords: peptide purity verification · HPLC purity assay · LC-MS identity · research peptide COA · RP-HPLC 214 nm