Quick PSA: Why your peptide COA needs BOTH HPLC and LC-MS (and how to verify it)

Hi fellow researchers,

I see a lot of questions lately about how to verify peptide quality, so I wanted to put together a quick checklist based on my own sourcing experience. If you’re buying research peptides, a Certificate of Analysis (COA) is your only real proof of quality—but you have to know how to read it.

A legitimate COA should always include:

1. Exact Batch/Lot Number: It must match the vial you received. Generic COAs are a massive red flag.

2. HPLC Data: To confirm chromatographic purity (ideally ≥98%), complete with the actual chromatogram graph, not just a number.

3. LC-MS/MS Data: To confirm the molecular mass and identity. HPLC alone cannot prove what the molecule is.

4. Independent Lab Name: The testing should be done by a verifiable, third-party laboratory, not "in-house."

Transparency is everything in this space. I’ve found that reputable suppliers, like [Windy City Peptides](https://windycitypeptides.com/), make it a standard practice to provide clear, batch-specific documentation for their high purity research peptides, which takes the guesswork out of the equation.

Always remember: if a supplier is hesitant to provide a full, batch-specific COA upon request, walk away.

What else do you all look for when vetting a new supplier?