Reading an HPLC Report
A purity percentage on its own tells you very little. What makes a batch report meaningful is whether you can tie it to the vial in your hand, and whether you understand which question the number actually answers.
What HPLC does
High-performance liquid chromatography drives a dissolved sample under pressure through a column packed with a fine stationary material. Different components travel through at different speeds depending on how strongly they interact with that packing, so they emerge separated in time.
A detector at the outlet records what comes off and when. The output is a chromatogram: a trace with peaks, where each peak is a component and the area under it is proportional to how much of that component was present.
Reading the chromatogram
The target peptide is normally the dominant peak. Purity is expressed as that peak's area as a proportion of total peak area across the run.
Two figures answer two different questions and they are routinely conflated:
| Figure | Question it answers |
|---|---|
| Purity (%) | Of the material present, how much is the target compound? |
| Content (mg or mg/ml) | How much target compound is actually there? |
A vial can report 99 percent purity and still contain less peptide than stated. Purity is about what else is in there; content is about quantity. A complete report gives both.
Nominal against measured
Where a report states a content figure, expect it to differ slightly from the label. A 20mg pen in 3ml is 6.67mg/ml by arithmetic, and a measured 6.52mg/ml is 97.8 percent of that. Small shortfalls are normal in manufacture.
A result meaningfully above nominal deserves more scrutiny than one slightly below, since it usually indicates a fill or concentration error rather than good news.
The part that actually matters
Match the batch identifier. A report describes one specific batch. If the identifier on the certificate does not match the one printed on your vial, the report tells you nothing about what you are holding, however good the numbers look.
This is the single most common failure in practice. A supplier displays an impressive chromatogram, the batch reference does not correspond to the stock being sold, and nobody checks.
Check in this order:
- Batch or lot identifier on the report against the vial or pen label.
- Compound name and stated strength.
- Test date, and whether it precedes manufacture of your batch.
- Testing laboratory named, not merely implied.
- Both purity and content present rather than purity alone.
Independent testing
A report from the manufacturer's own laboratory is not worthless, but it is not independent. The value of third-party testing lies in the sample being submitted separately and analysed by an organisation with no stake in the result.
Some third-party laboratories publish results against a lookup key, so a report can be verified at source rather than taken from a supplier-hosted image. Where a key is provided, use it. A PDF can be edited; a database entry at the testing laboratory cannot be, at least not by the seller.
What a report does not tell you
- Sterility. HPLC measures chemical composition, not microbial contamination.
- Endotoxin levels. A separate test entirely.
- Handling since testing. A batch tested at manufacture says nothing about whether it has since been frozen, overheated or left in sunlight.
- Your specific vial. Testing is per batch, not per unit.
That last point is why storage discipline still matters on a batch with an excellent report. See storage and stability.
Frequently asked
Is 99 percent good? For a research peptide, high purity is normal rather than exceptional. A figure that is meaningfully lower is worth questioning; a very high one is not by itself remarkable.
Can a report be faked? An image can. That is the argument for verification keys that resolve at the testing laboratory rather than at the seller.
Why do purity and content differ? Because they measure different things. Purity is a proportion, content is an amount.