A peptide can be very pure and still be the wrong peptide. That sounds strange, so let us unpack it — in plain English.
Purity vs. Identity
There are two different questions a good lab report answers:
- Purity = how clean is it? (Covered in what purity means.)
- Identity = is it actually the molecule the label says?
You could have a jar that is 99% full of a single, very clean substance — but if it is the wrong substance, the purity number does not help you. That is why identity gets its own test.
The "Fingerprint" Check
To confirm identity, labs use a tool called a mass spectrometer. In simple terms, it weighs the molecule very precisely. Every peptide has a known, expected weight based on its recipe. If the measured weight matches the expected weight, the identity is confirmed — a bit like matching a fingerprint or a DNA test.
If the weight is off, it is a red flag. It could mean the peptide is missing a piece, has something extra attached, or is simply not what the label claims.
What This Looks Like on a COA
On the lab report you will usually see two weights side by side: the expected weight and the found (measured) weight. When they match closely, the peptide's identity checks out. You do not need to do any math — you are just looking for "these two numbers agree."
Why It Matters
Purity and identity work as a team. Purity says "it's clean," identity says "it's the right thing." A trustworthy COA shows both. If a document only shows a purity percentage and never confirms identity, that is worth questioning.
Common Questions
Do the two weights have to match exactly? They need to match within a small, normal margin — instruments are not infinitely precise, and that is expected.
Is identity more important than purity? Neither replaces the other. You want both confirmed.
New here? Begin with what a COA is, then see how to read one step by step.
Sources
- U.S. Food & Drug Administration / ICH Q6A — identity and testing standards
- U.S. Pharmacopeia — peptide quality testing standards
Research Use Only. Not for human or animal consumption. This article explains lab paperwork for laboratory research and is not medical, dosing, or usage advice.
