How to Write a Peptide RFQ That Produces Comparable Quotes

The problem with three quotes that don't match

Ask three suppliers to price the same peptide and you will often get three numbers that share almost nothing. One quotes crude material, another quotes it purified past a threshold you never named, and a third quotes a salt form and counterion you did not expect. The spread looks like a commercial difference. It is usually a specification difference in disguise, and it means the cheapest quote may be the one that leaves the most work undone after delivery.

The fix is not more negotiation. It is a request for quotation that pins down every variable that moves the price, so that when quotes diverge you are comparing suppliers rather than comparing your own ambiguity. A good RFQ front-loads the decisions you would otherwise be forced to make later, under time pressure, once material is already in hand.

Treat the RFQ as the first draft of the specification you intend to hold the supplier to. Anything you leave vague becomes a place where a supplier can quote optimistically and deliver something technically defensible but wrong for your use.

There is a second, quieter benefit. A precise RFQ is a filter: suppliers who cannot meet a clearly stated requirement tend to say so at the quoting stage rather than after they have your order. The ambiguity you remove up front does not just make the quotes comparable, it surfaces the mismatches while they are still cheap to walk away from.

Sequence and identity: remove every reading

Start with the sequence written in unambiguous one-letter or three-letter code, in an explicit N-to-C orientation. Spell out every modification: N-terminal acetylation, C-terminal amidation, cyclization and the atoms that close the ring, disulfide connectivity when more than one topology is possible, and any non-natural or D-amino acid residues. Stereochemistry that is implied but not stated will eventually be read the wrong way by someone.

Label conjugates and tags with the same discipline. A biotin, a fluorophore, or a chelator changes the synthesis, the purification behavior, and the analytical burden, and each needs its attachment position and linker defined. If a dye has multiple isomers or a linker has multiple lengths, name the one you want.

Where a public identifier exists, cite it, but do not let an identifier replace the written sequence. Identifiers can be transcribed incorrectly or point to a variant. The written sequence is the contract; the identifier is a convenience cross-check.

It also helps to state how you expect identity to be confirmed on delivery. Mass spectrometry establishes the molecular mass, but mass alone does not distinguish sequence isomers or resolve certain modifications, so if your peptide has an ambiguity that mass cannot settle, name the orthogonal check you expect. Deciding that now avoids the argument later about whether a certificate that reports only a mass has actually proven you received the right molecule.

Physical form, salt, and counterion

The form you receive changes both the mass you can weigh out and the price you should expect. State whether you want a lyophilized powder or a solution, and if a solution, the solvent and target concentration. Name the salt form and counterion explicitly, because trifluoroacetate, acetate, and hydrochloride behave differently and a residual counterion can interfere with sensitive assays.

Net peptide content matters as much as gross mass. Two vials labeled with the same milligram figure can contain very different amounts of actual peptide once water, counterion, and residual solvent are subtracted. Ask for quantity on a net-peptide basis, and ask how that net content is determined so you can compare like with like.

Quantity, purity, and the test panel

Quantity and purity are coupled. Requesting higher purity at larger scale can require additional purification passes and lowers usable yield, so state both together and, where you can tolerate it, give a range rather than a single hard number. A supplier who knows your true tolerance can offer a more honest price than one guessing at your intent.

Define the analytical panel rather than assuming a standard one exists. At minimum, most research peptide work benefits from an identity confirmation by mass spectrometry and a purity determination by a stated chromatographic method with a defined wavelength and gradient family. Beyond that, decide whether you need counterion content, water content, residual solvents, endotoxin, or net peptide content, and say so. Each added test has a cost and a turnaround implication.

Ask for the deliverable that proves the panel was run: a certificate of analysis with the method, the acceptance criterion, and the result for each attribute, plus the supporting data files where relevant. Guidance on how specifications and acceptance criteria are constructed for drug substances gives a useful mental model even when your material is for research, because it separates the attribute, the procedure, and the limit into three distinct decisions.

• Identity: confirmed by a named method against the expected mass.
• Purity: reported by a stated method, wavelength, and gradient, with the acceptance limit written out.
• Content: net peptide content and, where relevant, water and counterion.
• Safety-adjacent attributes: endotoxin or residual solvents only when your application requires them.

Packaging, aliquoting, and labeling

How the material is split affects both usability and cost. A single large vial is cheaper to fill than twenty aliquots, but if your workflow needs single-use portions, that saving disappears the first time you thaw and refreeze a shared vial. State the number of vials, the target fill per vial, the container type, and the closure, and note any inert-atmosphere or light-protection requirement.

Specify the label content you need and the format that your systems can read. If you require a lot number, a use-by or retest date, storage conditions, and a machine-readable code, put that in the RFQ so it is priced rather than negotiated after the fact.

Schedule and destination

A quote without a lead time is only half a quote. Ask for the realistic delivery window for the requested scale and purity, and ask separately what an expedited option costs, because expediting a difficult purification is not always possible at any price. Distinguish the synthesis and purification time from the shipping time so you can see where the schedule risk sits.

Destination and handling drive real cost. A peptide that must ship frozen to a distant site carries packaging, coolant, and monitoring costs that a room-temperature shipment does not. Name the destination, the acceptable transit temperature, and whether you need shipment tracking, so cold-chain expectations are quoted rather than assumed. Recognized storage and distribution practices frame temperature control as a defined requirement rather than a courtesy, and your RFQ should treat it the same way.

Commercial assumptions that change the number

Two quotes at the same headline price can carry very different obligations once shipping terms are settled. State the Incoterms rule you want quoted against so the division of freight, insurance, customs, and risk is identical across suppliers. Without a named term, one supplier prices delivery to your bench and another prices handover at their loading dock, and you will not know until the invoices arrive.

Make the rest of the commercial frame explicit too: currency, validity period of the quote, payment terms, and what happens if a lot fails the agreed specification. A clear remedy for out-of-specification material, agreed before purchase, is worth more than a small unit-price saving.

Keep a clarification log

Questions will come back, and the answers change the meaning of the quotes. Keep a single clarification log that records each question, the supplier who asked it, the answer you gave, and the date. When you circulate an answer that affects the scope, send it to every supplier so they all price the revised assumption.

The log does more than keep the bid fair. It becomes the written record of what everyone understood at award, which shortens the argument if a delivered lot does not match expectations. An RFQ that produces comparable quotes is really an RFQ that removed the ambiguity before anyone put a number on paper.