Every batch that reaches this catalogue is tested twice, by two different methods, for two different things. Purity is one question and identity is another, and a compound can pass one while failing the other.
What gets tested
Purity is measured by high performance liquid chromatography. Identity is confirmed by mass spectrometry. Both are run on the batch you are being sold rather than on a representative sample from a previous lot, and both results appear on the certificate that ships with your order.
A batch that fails either test is not released. It does not get sold at a discount, it does not get blended into another lot, and it does not sit in stock waiting for someone who might not check. That is the most important sentence on this page.
Reading a certificate of analysis
Most suppliers will send you a certificate. Fewer will explain what is on it, which makes the document harder to use than it should be. Here is what to look at, in order.
The batch reference
Top of the sheet, usually alongside the date of manufacture. Check it matches the number printed on the label of the vial in front of you. If it does not, the certificate belongs to a different lot and tells you nothing about what you are holding. This sounds obvious and it is still the most common mismatch we get asked about.
The chromatogram
A trace with one dominant peak and a flat baseline either side. The area under the main peak, as a percentage of total peak area, is the purity figure. What you want to see is a single clean peak rather than a cluster of smaller ones. Several peaks of similar size means the sample contains several things.
The purity figure
Usually stated as a percentage against HPLC. A figure of 99 percent means 99 percent of the detected material was the target compound. It does not mean the remaining one percent is inert, and it does not tell you what the remaining one percent is. For most laboratory work that distinction does not matter. For some it does, and if it matters for yours, ask.
The mass spectrometry result
This confirms identity. The observed molecular weight should match the theoretical weight for the compound within a small tolerance. If the purity figure is high but the mass does not match, you have a pure sample of something else.
The dates
Date of manufacture and date of analysis. Shelf life runs from manufacture, not from the day the parcel arrives.
What a certificate does not tell you
It does not tell you how the compound was handled between the laboratory that tested it and your bench. That is a supply chain question rather than an analytical one, and it is where most degradation actually happens. Our answer is cold chain shipping on the items that need it, and a specification table on every product page stating the condition that applies to that compound.
Traceability
The batch reference is recorded against your order at dispatch. A result you generate months from now can be tied back to a specific lot and its paperwork, which matters if you ever need to explain a discrepancy or repeat a piece of work with the same material.
Questions worth asking any supplier
Can I see the certificate before I order. Is it for this batch or a previous one. What happens to a batch that fails. How is the compound shipped and at what temperature. If a supplier is slow to answer any of those, that is information in itself.