1. Demand an independent, third-party Certificate of Analysis
The single most important signal is a batch-specific Certificate of Analysis (COA) from an accredited, independent laboratory — not the manufacturer's own in-house test. An in-house COA introduces a conflict of interest.
The strongest suppliers publish a public COA library so you can verify identity and purity before you buy, and ship a lot-specific COA with every order.
2. Confirm both HPLC and mass spectrometry
Two analytical methods matter, and they answer different questions. HPLC (high-performance liquid chromatography) measures purity — what percentage of the sample is the target compound. Mass spectrometry (MS / LC-MS) confirms identity — that the molecular weight matches the intended peptide.
A COA with only one method is incomplete. Look for both, with stated acceptance criteria, not just a logo.
3. Check the purity threshold — and what happens below it
The serious suppliers hold a ≥99% purity threshold and destroy below-spec lots rather than selling them. Many vendors quietly accept 98% as 'industry standard.' Ask what their threshold is and what they do with lots that miss it.
4. Look for cold-chain handling
Lyophilized peptides are sensitive to heat and humidity. Suppliers shipping at 2–8°C with a temperature log demonstrate they understand reagent integrity. A transit temperature record appended to the COA lets you audit the conditions your material actually experienced.
5. Verify a real U.S. business and responsive support
A legitimate supplier discloses a physical U.S. address, answers documentation requests in hours, and doesn't communicate only through encrypted messaging apps. Responsiveness to a COA request is a fast, revealing test.
6. Read the compliance posture
Reputable research suppliers sell strictly for Research Use Only, enforce an age gate and a research-use certification at checkout, and make no therapeutic or dosing claims. A vendor making health claims is both a regulatory risk and a credibility red flag.
See it in practice
Every Ethos Bio compound ships with an independent, mass-spec-verified Certificate of Analysis. Browse the public COA library.
Frequently asked questions
What is the most important thing when choosing a peptide supplier?
An independent, third-party, batch-specific Certificate of Analysis (COA) with both HPLC purity and mass-spectrometry identity confirmation. In-house-only COAs carry a conflict of interest; a public COA library you can check before buying is the strongest signal.
What purity should research peptides be?
Leading suppliers hold a ≥99% HPLC purity threshold and destroy below-spec lots. Many vendors accept 98% as standard, so confirm the threshold and the disposition of failing lots.
Why does cold-chain shipping matter for peptides?
Lyophilized peptides degrade with heat and humidity. Shipping at 2–8°C with a continuous temperature log, ideally appended to the COA, lets a researcher audit whether reagent integrity was maintained in transit.