How to read a Certificate of Analysis
A Certificate of Analysis is the record that connects the material you received to the specification you agreed. It is not a general quality statement about the supplier, and it is not interchangeable between batches. Most disputes about peptide deliveries come down to a COA being read as something it is not.
It describes one batch
Every result on a COA belongs to the batch named on it. A COA from a previous batch tells you nothing about the material in front of you, however similar the product. The first check is therefore the simplest one: does the batch number on the document match the batch number on the container?
The fields that have to match your order
- Product name and, where relevant, sequence
- Batch or lot number, matched against the container and the packing record
- Quantity and product form
- The specification the batch was tested against
- Date of manufacture or analysis, and any retest or use-by date
These should agree with your order confirmation. If any of them differ, resolve that before looking at the results, because a mismatch here means you may be reading a document for different material.
Results are only meaningful with their method
A purity figure on its own is not comparable between suppliers. Purity by HPLC depends on the method, the column, the gradient and the detection wavelength, and two laboratories reporting the same number under different methods are not reporting the same thing. A COA should name the method for each result. If it does not, the figure cannot be checked and should not be used for comparison.
Net peptide content versus gross weight
Peptides are usually supplied as a salt and carry residual moisture, so the mass in the container is not all peptide. If your order was quoted by net peptide content and the COA reports gross weight, or the reverse, the quantities will not reconcile. This is worth checking explicitly rather than assuming.
What a COA does not tell you
It reports what was tested. Anything outside the agreed specification was not measured, and its absence from the document is not evidence of anything. If a property matters to your application, it belongs in the specification before production, not in a request after delivery.
Before you accept the batch
Check the batch number against the container. Check the identifying fields against your order confirmation. Check that each result names its method. Check that the quantity basis matches how the order was quoted. If the document arrived from an address you do not recognise, verify the sender before acting on it.
The documents page lists the other records that may accompany an order, and quality & documentation covers how the records should agree with each other.