How to vet high quality peptides for sale: ≥98% HPLC purity, MS identity, lot-specific COA, net peptide content, cold chain, and $40–$180 vial pricing.
Buying high quality peptides for sale as reference material comes down to five verifiable things: HPLC purity stated as a number (≥98% is the working floor, 99%+ for analytical standards), identity confirmed by mass spectrometry against the theoretical monoisotopic mass, a lot-specific certificate of analysis dated within the life of that batch, disclosed net peptide content rather than gross vial mass, and cold-chain handling with a traceable lot number printed on the vial itself. Anything missing one of those is an unqualified material, regardless of the marketing around it. Expect to pay roughly $40–$180 per vial for documented research-grade material, and expect the documentation — not the compound — to be what you are actually paying for. Everything sold under these terms is research use only.
The phrase is meaningless as a claim and precise as a measurement. A COA that supports it contains, at minimum: the analytical method and its parameters, the purity result expressed as area percent, the mass spectrometry result with observed versus theoretical mass, the lot number, the manufacture date, the retest or expiry date, and the name of the lab that ran the assay.
What disqualifies a document immediately:
A supplier who runs analytics properly will hand over the raw chromatogram and the mass spec report as separate files without being pushed. Ours are published per lot on the quality page.
This is the single most consequential figure on a spec sheet, and it is routinely omitted. A vial labeled 10 mg contains 10 mg of lyophilized powder — not 10 mg of peptide. The remainder is counterion salt, residual water, and residual solvent.
Trifluoroacetate from reverse-phase purification typically accounts for 8–22% of gross mass depending on the number of basic residues in the sequence. Residual water measured by Karl Fischer runs 3–8% in a properly lyophilized cake. Stack those and net peptide content commonly lands between 70% and 85% of the labeled mass, even in material that is genuinely 99% pure by HPLC.
Those two numbers describe different things and are constantly conflated. HPLC purity says: of the peptide-related material present, 99% is the target sequence. Net peptide content says: of the total powder mass, this fraction is peptide at all. A supplier can be honest about the first and silent about the second, and most are.
Purity tells you what fraction of the peptide is the right peptide. Net content tells you how much peptide is in the vial. A material can be 99% pure and still be 28% salt and water by weight.
If your work requires gravimetric accuracy, ask for net peptide content by amino acid analysis or quantitative NMR before purchase. If the answer is "we don't test for that," you now know the grade you are buying, which is still useful information.
The area-percent figure at the top of a COA depends entirely on the method that produced it, and methods can be tuned to flatter a sample. Look for these parameters:
A useful question for any supplier: what is your column lifetime policy? A C18 column used for peptide QC degrades measurably after roughly 1,000–1,500 injections, and resolution drifts before failure is obvious. Labs that replace on a schedule produce comparable data across lots; labs that run a column until it visibly fails produce a purity number that quietly means something different in month 14 than it did in month 2.
ESI-MS or MALDI-TOF answers one question: is this the sequence claimed? A well-run report gives the theoretical monoisotopic or average mass and the observed mass, and the two should agree within ±0.5 Da for monoisotopic and ±1–2 Da for average mass on a standard instrument.
Mass spectrometry will not catch a diastereomer, will not distinguish isobaric substitutions such as Leu for Ile, and is not a quantitative purity method. A supplier presenting an MS report as proof of purity has either misunderstood their own data or is counting on you to. You need both assays. Neither substitutes for the other.
Lyophilized peptide stored at -20°C in a sealed, desiccated vial is the standard condition, with -80°C used for long-term archival of sensitive sequences. Refrigeration at 2–8°C is acceptable for short holds. Typical stated shelf life for lyophilized material under proper conditions is 24–36 months from the manufacture date.
That claim is only meaningful if two things are true. First, the clock started at manufacture, not at shipment — ask for the manufacture date, not just an expiry. Second, the cold chain held in transit. Ask what the packaging is and how long transit takes; 2–5 business days with cold packs is a different exposure profile than 10 days in a mailer sitting in a July delivery vehicle. Our handling and transit terms are on the shipping page.
Sequences containing Met, Cys, Trp, or N-terminal Gln carry known chemical liabilities — oxidation, disulfide scrambling, pyroglutamate formation — that no storage temperature fully eliminates over multi-year holds. A supplier who tells you every product is equally stable for 36 months has not thought about it.
This section costs us sales, and it should.
The honest limitation of any COA: it describes the material at the moment of testing, from a sample of that lot, under that lab's method. It is evidence, not a guarantee, and it says nothing about the vial in your hand after it has been shipped, thawed, and opened. Retention samples and a documented chain of custody narrow that gap; nothing closes it.
Spend 30–60 minutes on this before releasing a PO, and repeat it annually:
For repeat or program-scale purchasing where lot reservation and consistent batch documentation matter more than unit price, the wholesale terms are the relevant path, and lot-hold requests can be arranged through contact.
The material is a commodity. The paperwork is not. Buy the paperwork.
Supplied strictly for in-vitro laboratory research by qualified researchers and institutions. Not a drug, food, cosmetic or dietary supplement. Not for human or veterinary consumption. Not evaluated by the FDA.
Purity, identity and lot number, documented for the exact vial you receive.