How to read a certificate of analysis
Most people buying a peptide receive a certificate of analysis with it, and most have never been shown how to read one. It is a genuinely useful document. It is also narrower than it looks, and the gap between what it proves and what people assume it proves is where confusion lives.
What the sections mean
Identity, usually by mass spectrometry
Mass spectrometry measures the molecular weight of what is in the sample and compares it with the expected weight of the peptide. A match is good evidence that the molecule is the one named. This is the part of the document doing the most work, because it answers the question most people actually have: is this the right compound?
Purity, usually by HPLC
High performance liquid chromatography separates the sample into its components and reports each as a percentage of the total. A figure such as 99.1% means the main peak accounts for that share of what was detected. It does not mean the remaining 0.9% was identified, and it does not describe what those other peaks are unless the report says so.
Net peptide content, which affects your arithmetic
This is the line most worth understanding, and it is often missing. Synthetic peptides are usually supplied as a salt, commonly with trifluoroacetate, and they hold water.A vial weighed at 5 mg may therefore contain less than 5 mg of the peptide itself. Where a report distinguishes gross weight from net peptide content, the net figure is the one that matters for working out concentration.
Our reconstitution calculator uses the number you enter. If your certificate reports a net peptide content lower than the labelled weight, that is the number to use.
Batch or lot number, and date
A certificate describes one batch, tested on one date. The batch number on the document and the batch number on the vial should be the same. A certificate for a different batch is a document about a different production run.
What a certificate does not cover
- Sterility. Standard purity testing is not a sterility test. Unless the report names a sterility or bioburden method, it has not been assessed
- Endotoxins. A separate test, usually absent unless specifically commissioned
- The exact amount in your vial. Fill accuracy is a different measurement from purity
- Whether the compound works. Nothing in a chemical analysis speaks to clinical effect
- Whether it is lawful where you are. A pure compound and a legal one are unrelated questions
Three different questions, three different answers
| Source | Answers | Cannot tell you |
|---|---|---|
| Certificate of analysis | Is this the molecule claimed, at what purity, in this batch | Whether it works, whether it is safe over time, whether it is legal |
| Evidence rating | How strong the human evidence is that it does what it is used for | Anything about the vial in your hand |
| Safety Confidence | How well the safety profile is characterised | Anything about the vial in your hand |
A clean certificate and a one star evidence rating are not in conflict. A compound can be exactly what it claims to be and still have no human trials behind it. Those are separate facts, and holding both at once is the whole skill.
Checking a certificate independently
Documents can be reissued, edited or attached to the wrong batch, sometimes without anyone intending harm. If a certificate matters to a decision, the straightforward step is to take the report number and the batch number to the laboratory named on it and ask them to confirm the result. Testing laboratories in this field are used to that question.
Independent testing commissioned by the buyer, rather than the seller, is the other route, and several laboratories offer it directly to individuals.
Educational reference, not medical advice, and not a recommendation to use or obtain any compound. Laboratory methods and reporting conventions vary, so the report in front of you is the authority on what it did and did not measure. Edition 1.0.