Start with the Certificate of Analysis
The single most important thing a research-peptide vendor can give you is a batch-specific Certificate of Analysis (COA) from an independent, accredited laboratory. A COA reports the identity and purity of the exact lot you are buying — not a generic marketing figure. Before you buy from any vendor, confirm they publish a COA for the specific lot, and that the lot number on the COA matches the product.
A purity percentage on its own is a claim; a purity percentage backed by an HPLC chromatogram and a mass-spec identity result is a measurement. Prefer vendors who show the supporting analytics, not just a number.
Look for independent, third-party testing
Third-party testing means the analytical work is done by a laboratory the vendor does not own — ideally an ISO 17025-accredited facility. That independence is what makes a purity or identity result credible. Vendors that test in-house only, or that cannot name their lab, are harder to verify.
The vendors compared on this site publish third-party COAs and test each batch; always open the vendor product page and read the current lot’s documentation before purchasing.
Prefer US-based sourcing and clear handling
US-based vendors generally ship faster, handle cold-chain logistics more predictably, and are easier to reach for support. For lyophilized research peptides, look for vendors that describe their storage and shipping (for example, shipping cold with insulation) so material arrives in good condition.
Compare prices across vendors before you buy
Prices for the same compound vary widely between suppliers. On this site, every product page shows a live "Where to buy" comparison — the vendors that carry it, their scanned prices, and a direct link to each. Use it to find the current lowest price and any applicable code before you order.
Remember that the cheapest listing is not automatically the best value: weigh price against the COA, testing, and stock status shown for that vendor.