How to verify a blend COA when there is no single molecule
Every COA convention assumes one compound. Blends break all of them. What purity, mass confirmation and peptide content mean when a vial holds three peptides.
Certificate of Analysis conventions assume a vial holds one compound, and a blend breaks every one of them. Purity has to be reported per component, mass spectrometry needs one confirmation per peptide, and there is no single molecular weight or CAS number to check against. A blended figure describes nothing.
By the Bench Grade Research Team ·
Why single-compound conventions fail here
An HPLC area percent describes the fraction of detected material eluting as the main peak. In a three-component vial there is no main peak — there are three, by design. A supplier reporting one purity number for a blend has either measured one component and labelled it as the whole, or produced a figure that corresponds to nothing.
The same problem applies to peptide content. Amino acid analysis returns amounts of amino acids, and in a mixture those come from several sequences at once, so attributing them back to components requires the composition to be known and the calculation to be done deliberately.
What a defensible blend COA contains
- A chromatogram showing resolved peaks for every component, with each identified.
- An area percent for each component individually.
- One mass-spectrometry confirmation per component, matched against that peptide's expected molecular weight.
- The per-component mass split in milligrams, not only the total.
- A lot number matching the vial, and an independent laboratory's signature.
Questions that separate real analysis from a forwarded document
Ask which peaks correspond to which component. Ask whether the method was developed for this blend or adapted from a single-compound assay. Ask what the per-component masses are. These have specific answers if the work was done, and produce hedging if the document was passed along from a supplier upstream.
The identity checks that do not exist for a blend
A single peptide can be checked against a CAS Registry Number and one molecular weight. Neither exists for a mixture, so those two checks — the fastest and most decisive available for a single compound — are simply unavailable. What replaces them is per-component verification, which is more work and is why blend documentation is more variable across suppliers than single-compound documentation.
Frequently asked questions
- Can a peptide blend have a CAS number?
- No. A CAS Registry Number identifies one distinct substance, and a mixture of peptides is not one substance. Only the individual components have CAS numbers, so identity has to be checked component by component.
- What purity figure should a blend COA show?
- One per component, not a single number for the vial. In a multi-component blend there is no single main peak, so a lone area-percent figure either describes one component mislabelled as the whole or corresponds to nothing.
- How many mass spectrometry results should a blend COA have?
- One per component. A three-peptide blend needs three confirmations, each matched against that peptide's expected molecular weight, because the mixture has no molecular weight of its own.
Compounds discussed in this guide
More on quality control
- What is in a peptide stack, and what the research coversA stack is several separate vials bought together, not a mixed product. What each of ours contains, and why the literature belongs to the components.
- How to read a peptide Certificate of Analysishow to read a Certificate of AnalysisThe five numbers that actually matter on a peptide COA, what they mean, and the red flags that should make you choose a different supplier.
- HPLC vs mass spec vs amino acid analysis — what each test provesA practical guide to the three peptide QC methods, what each can prove and disprove, and why a complete QC profile requires all three.
All products discussed in this guide are supplied by Bench Grade Peptides for laboratory research use only. Not for human or veterinary use.