Reading certificates and vial labels
Paperwork is the only piece of a purity claim open to your own checking. This page shows you how.
- What is a Certificate of Analysis (CoA)?
- Does each lot need its own certificate?
- What should you check on a CoA?
- Why are lot numbers so important?
- What is a lot number for?
- What can a CAS number tell you, and what can't it?
- What is a CAS number?
- What should a good lab record include?
- What belongs on a peptide vial label?
What is a Certificate of Analysis (CoA)?
A CoA is the test record for a single batch. It says what was tested, which lab did it, when, and what the results were. It always belongs to one batch. A certificate with no lot number attached does not describe any real material.
Does each lot need its own certificate?
Yes. One certificate covers one batch, so every new batch needs a fresh one. If a supplier shows the same certificate for several lots, that document no longer tells you what is in your vial. A certificate per lot is the minimum standard, not an extra.
What should you check on a CoA?
Five points. First, the lot number matches your vial. Second, the testing lab is named and independent. Third, an HPLC purity figure is given. Fourth, identity is confirmed, through mass spectrometry or an HPLC run compared with a reference standard. Fifth, a recent test date is shown. If the lot number differs from your label, the whole document is about some other material.
Why are lot numbers so important?
They are what make tracing possible. If a result looks odd, the lot number shows whether other experiments share that batch. When a batch gets recalled, it pinpoints which material is involved. Take lot numbers away and no quality question can be answered.
What is a lot number for?
It names one production batch. It is the link between a physical vial and its test results. The number on the label should also appear on the certificate. Without that link, nothing proves the certificate in front of you describes the material you are holding.
What can a CAS number tell you, and what can't it?
It tells you which substance is meant. Nothing more. It identifies the compound as a concept. It reveals nothing about how pure, how good or how well stored the contents of a particular vial are. Treat it as a naming tool, never as a sign of quality.
What is a CAS number?
It is a unique ID that the Chemical Abstracts Service gives to one specific chemical substance. Its job is to end confusion over names. A compound can go by many names and spellings, but it has only one CAS number. That makes it a dependable key for finding literature.
What should a good lab record include?
Log the lot number with every result, not just the compound name. Add the reconstitution date, the diluent, the concentration and the storage conditions. If a result looks strange later, these notes let you separate a real experimental effect from a material or handling problem.
What belongs on a peptide vial label?
Four things: the compound name, the amount in milligrams, its lot number, and a note that it is for research use. Check the lot number first. It is what ties the vial to its certificate. The milligram figure refers to the peptide alone, not to the total weight of powder in the vial.