What Should You Ask a Peptide Supplier?

Why a checklist is more useful than a catalog

A supplier checklist is not a bureaucratic ritual. It is a way to move the commercial conversation onto technical ground, where vague answers become visible. Most procurement failures in this industry do not begin with a bad batch arriving. They begin with a specification that was never written down, a sequence that was never reviewed, and a certificate of analysis that nobody compared with the lot label.

The twelve questions below are grouped in four blocks: who the supplier legally is, what it can actually make, how it proves what it made, and how it behaves when something goes wrong. A supplier can pass the first block with paperwork and the second with a brochure. The third and fourth blocks require batch records, retained samples and a quality system, which are much harder to fabricate.

Score the answers rather than reading them. A complete answer names a person, a method, a document and a date. An incomplete answer uses the word "standard" without defining it.

Questions 1 to 4: identity, capability and sequence review

The first four questions establish whether you are dealing with a manufacturer, a disclosed trading partner or an anonymous broker. None of those is automatically disqualifying, but the answer changes how much verification you need to do later.

• 1. What is your registered legal name and manufacturing site? The website name, the invoice beneficiary and the COA signatory should match. Ask for the business license or registration number and the address where synthesis actually happens.
• 2. Who reviews my sequence before quoting? A chemist should comment on length, hydrophobicity, cysteine pattern, aggregation risk and modification compatibility. A salesperson reading a price table cannot do this.
• 3. Which synthesis route and resin will you use? Standard Fmoc SPPS covers most sequences. Long, cyclic or modified peptides may need pseudoproline dipeptides, a different resin or a hybrid route. The answer shows whether the process was chosen or defaulted.
• 4. Can you make this sequence at my scale, and what yield do you expect after purification? Yield after purification is the number that decides whether the delivered mass is realistic.

A supplier that answers all four in specifics is a supplier you can audit. One that answers only the first two is a sales channel.

Questions 5 to 8: purity, COA, traceability and retention samples

Purity is the most quoted and least comparable number in peptide procurement. Two suppliers can report 95% for the same sequence and mean different things, because the figure depends on the column, gradient, wavelength, integration threshold and whether the sample came from the crude or the purified pool.

Ask for the method, not only the result. Reverse-phase HPLC at 214 or 220 nm is conventional for peptides, and the chromatogram should show the gradient, the retention time of the main peak and an integration table. Request the mass spectrum as well, with the deconvoluted mass and the observed error, so identity can be checked independently of the sequence you sent. The COA requirements guide lists every field a usable certificate should contain.

Traceability and retention come next. A lot number is only meaningful if it links to a synthesis record, a purification pool and a lyophilization cycle. Retention samples are the physical proof: if the supplier cannot pull material from your lot in six months, a later dispute becomes a conversation about storage conditions that nobody can win.

The twelve questions in one table

Send this table as a questionnaire. Written answers are comparable; verbal answers are not.

Questions 9 to 12: nonconformance, change control, lead time and documents

The last four questions separate a transactional seller from a supplier you can keep. Nonconformance handling is the clearest signal. Synthesis fails routinely, and a supplier that reports no deviations at all is not recording them. Ask what happens if the delivered lot misses the agreed purity: is there a written replacement or credit policy, and does the deviation report reach the customer?

Change control matters for repeat orders. If the resin supplier changes, if the site moves, or if the purification method is redeveloped, you should hear about it before the next batch ships, not after your assay drifts. A notification clause in the quality agreement covers this without adding bureaucracy.

Lead time should be quoted in working days from purchase order, with the starting event defined. Packaging should be specified down to vial size, closure, desiccant and labeling. Export documents are the final item: a commercial invoice, packing list, safety data sheet and certificate of origin are routine, and a supplier with export experience produces them without prompting. Our quality page describes how these controls work at MOL Changes.

What a good answer sounds like, and what deflection sounds like

A good answer is specific and falsifiable. "We use RP-HPLC at 220 nm on a C18 column, purity is area percent, and the chromatogram ships with the lot" can be checked. "High quality, best price, strict QC" cannot. When you ask about a difficult sequence, a good supplier says which part is difficult and what it will do about it: double coupling at a hindered residue, a pseudoproline to break a beta-sheet stretch, or a lower guaranteed yield.

Deflection has a pattern too. Answers arrive as attachments rather than sentences. Questions about the manufacturing site are met with a list of certifications. Requests for a retained sample are answered with a new quotation. None of this proves bad intent, but each response shifts risk onto you, and the checklist exists to make that shift visible before money changes hands.

If you are comparing two suppliers, send the same sequence, the same purity target and the same delivery destination to both, then compare the specifications line by line. The China sourcing guide applies the same method to cross-border suppliers.

How MOL Changes answers the checklist

MOL Changes is a custom peptide manufacturer in Changsha, China, producing from 5 mg to kilogram scale with HPLC purity up to 98%+. Every batch is released with a certificate of analysis, an HPLC chromatogram and a mass spectrum for that lot, and we discuss the synthesis route before you order rather than after.

We do not claim ISO or GMP certification. What we can document is the sequence review, the analytical data, the lot traceability and the export paperwork, and we will answer the twelve questions above in writing. Start with the custom peptide synthesis service page or send the checklist to our team.