What purity should research peptides be?

Better than 98% by RP-HPLC is the working expectation for synthetic research peptides, with mass spectrometry confirming identity. Below that, related-substance peaks can materially affect quantitative in vitro results.

What is the difference between a COA and third party testing?

A certificate of analysis is the document; third party testing describes who generated the data. The strongest position is a lot specific certificate produced by an independent laboratory that is named on the report.

Does peptide content matter as much as purity?

For quantitative work, yes. Purity describes the fraction of peptide material that is the target sequence, while peptide content describes how much of the vial's total mass is peptide rather than salts and residual water.

Procurement · 8 min read

How to evaluate a research peptide supplier

A practical checklist for assessing purity documentation, lot traceability, storage handling and analytical independence before placing an institutional order.

Start with the certificate, not the price

The single most informative document a supplier can give you is a certificate of analysis tied to the exact lot you will receive. A generic COA for the compound — not the lot — tells you nothing about the vials in the box. Look for the lot number printed on the vial appearing on the certificate, and for a report date that precedes your order rather than following it.

A complete certificate carries an RP-HPLC purity chromatogram with the integration visible, a mass spectrometry result confirming the expected molecular weight, and the identity of the laboratory that performed the work. Purity stated as a bare number with no supporting trace is an assertion, not a measurement.

Independence of the testing laboratory

Third-party testing means the analysis was performed by a laboratory with no commercial interest in the result. In-house QC is valuable and most serious suppliers do both, but an in house number alone leaves the supplier grading its own work.

Named, verifiable laboratories are the standard to hold suppliers to. If a certificate carries no laboratory identity, no analyst signature and no instrument metadata, it cannot be independently checked and should be treated as marketing material.

Purity, content and net peptide weight

Chromatographic purity and peptide content are different measurements and are routinely conflated. Purity describes what fraction of the peptide-related material in the vial is the target sequence. Peptide content describes what fraction of the total vial mass is peptide at all, with the remainder being counter-ions, residual water and salts.

A vial can be 99% pure by HPLC and still contain meaningfully less than its labelled mass of peptide. For quantitative work, ask whether the labelled strength is gross mass or net peptide weight, and be sceptical of any supplier that cannot answer that question directly.

Handling, packaging and the questions worth asking

Lyophilized peptides are stable at ambient temperature for short transit windows, but repeated thermal cycling is cumulative and invisible. Ask how material is stored before dispatch and what the supplier's policy is when a shipment is delayed in transit.

Four questions separate serious suppliers from resellers: can you send the COA for the lot I will receive, which laboratory performed the analysis, is the labelled strength net peptide weight, and what is your process if a lot fails re-assay. Vague answers to any of these are informative.

Frequently asked questions

What purity should research peptides be?: Better than 98% by RP-HPLC is the working expectation for synthetic research peptides, with mass spectrometry confirming identity. Below that, related-substance peaks can materially affect quantitative in vitro results.
What is the difference between a COA and third party testing?: A certificate of analysis is the document; third party testing describes who generated the data. The strongest position is a lot specific certificate produced by an independent laboratory that is named on the report.
Does peptide content matter as much as purity?: For quantitative work, yes. Purity describes the fraction of peptide material that is the target sequence, while peptide content describes how much of the vial's total mass is peptide rather than salts and residual water.