Verifying a
supplier before
the first order.

Peptide sourcing has a structural problem: the difference between a manufacturer, a trading company with a good web designer, and a reseller quoting from a competitor's price list is not visible from a website. It becomes visible after the third order, when something goes wrong.

These six checks take about half an hour and can be done before any money moves.

1. Establish who you are actually buying from

Ask for the business licence and read the scope of business, not just the company name. A licence that covers “chemical products trading” is a different counterparty from one that covers “manufacture of pharmaceutical intermediates”. Neither is disqualifying — but you should know which you are dealing with, because the remedies when something fails are different.

Then check one thing: does the bank account name match the company name on the licence? If the invoice comes from one entity and the bank account belongs to another, stop and ask why.

2. Test the certificate of analysis

Do not read the COA — interrogate it. Send back two questions:

1. Can you send the HPLC chromatogram for this lot, with the gradient and wavelength?
2. What is the net peptide content of this batch, as a percentage of the powder?

A supplier who manufactures will answer within a day. A supplier who resells will either go quiet or send a generic PDF with no lot number. That single exchange is the most efficient filter in this entire list.

3. Compare the sample to the bulk quote

Order a small quantity first, then compare three things against the bulk offer:

Compare	What a switch looks like
Lot number on the COA	Sample and bulk lots have different numbers — normal — but the specification should be identical
Purity and net content	Sample at 99%, bulk at 96% is a sourcing switch, not a rounding difference
Appearance	Colour or caking changes signal a different drying step or a different source

Write the sample's specification into the purchase order for the bulk. If the bulk lot cannot meet it, you have found the problem while it is still cheap.

4. Use a third-party laboratory once

One independent test on the first commercial lot costs a few hundred dollars and settles the question permanently. Identity by MS, purity by HPLC, and — for anything going into a cell-based protocol — endotoxin by LAL.

This is not a vote of no confidence. It is cheaper than a failed batch, and it gives you a baseline that every later lot can be compared against.

5. Read the terms, and the paperwork

• Incoterms. FOB and CIF put different risks on you. Know which one you signed.
• What ships with the goods. COA and SDS should travel with the shipment; declarations should be issued before it leaves.
• What happens on a failed lot. Replacement, credit, or “send it back at your cost”? Get it in writing before the order.

6. Six red flags, in order of severity

1. No lot number on the COA. The document cannot be tied to the goods you received.
2. Payment to a personal account or to a third-party company.
3. Refusal to name the counter-ion (acetate, TFA, or none).
4. Purity quoted without a method, or “99.9%” on every product in the catalogue — real lots vary.
5. Documents offered “after payment”. Declarations that cannot be issued before the order usually cannot be issued at all.
6. Pressure to buy now. A manufacturer with a stocked catalogue does not need a countdown timer.

The purpose of due diligence is not to find a perfect supplier. It is to find out, cheaply, how a supplier behaves when something is imperfect.

What a good answer looks like

Ask for one lot's documentation set before ordering: COA with method and chromatogram, MS spectrum, SDS, and the specification the batch was released against. A supplier who sends all four, unprompted, has told you most of what you need to know.

You can see the format we use on any product page — GHK-Cu is a useful example, because it is a product where the certificate has to prove copper content, not just peptide purity. If the structure of that document makes sense to you, you will recognise it elsewhere.