Purity and lab tests
If you cannot check a purity figure, it is only marketing. Here is what each test behind the figure really measures.
- What does a 99% HPLC purity figure tell you?
- What does mass spectrometry measure?
- How does HPLC testing work?
- What does quality control cover?
- Why are HPLC and mass spectrometry both needed?
- When is testing truly third-party?
- Why should batches be consistent?
- How should an HPLC chromatogram be read?
- Why test for endotoxin?
- Does “research grade” mean anything?
- How can you check a purity claim yourself?
What does a 99% HPLC purity figure tell you?
It tells you that 99% of the material the detector picked up came out as the target peak during the separation. It is a ratio of peak areas, not a full breakdown of what is in the vial. It ignores water, leftover salts and, crucially, whether that peak is the right molecule. Identity needs its own test.
What does mass spectrometry measure?
It turns the sample into ions and measures their mass-to-charge ratio. For a peptide, this settles the identity question. Does the measured mass equal the mass worked out from the intended sequence? Put simply, HPLC shows how clean the sample is. Mass spectrometry shows what the sample actually is.
How does HPLC testing work?
HPLC stands for high-performance liquid chromatography. The sample is forced under pressure through a tightly packed column. Each component moves at its own pace, depending on how strongly it clings to the column material. So the components leave at different times. A detector logs each one as a peak. Comparing the peak areas gives the purity figure.
What does quality control cover?
Quality control means the checks a batch must pass before it is released. They cover identity, purity and appearance, plus sterility and endotoxin where those apply. What matters most is the record keeping. Each result is logged against a lot number. That way any single vial can be traced to the exact data behind its release.
Why are HPLC and mass spectrometry both needed?
Each one answers a different question, and neither can stand in for the other. HPLC splits a mixture and reports what share of it is the main component. That is purity. Mass spectrometry weighs the molecule and confirms it is the intended compound. That is identity. A sample can be 99% one substance and still be the wrong substance.
When is testing truly third-party?
When a lab with no stake in the outcome runs the test and issues the report itself. A certificate that carries the independent lab's own name and reference number qualifies. A supplier's in-house result, re-typed onto a branded template, does not. That holds however official the template looks.
Why should batches be consistent?
A result nobody can repeat is not much of a result. If material changes from one batch to the next, any difference you see could come from the batch, not from the variable you meant to test. Documentation per lot turns “same batch” into a recorded fact instead of a guess.
How should an HPLC chromatogram be read?
Retention time runs along the x-axis. Detector response runs up the y-axis. The tall peak is your compound, and its retention time should line up with the reference. Then look at three things. Is the baseline between peaks clean? Do small peaks crowd close to the main one? Is the main peak symmetrical? A shoulder or a trailing tail hints at an impurity coming off the column with it.
Why test for endotoxin?
Endotoxins are pieces of bacterial cell wall. They survive sterilisation and can skew biological assays. The usual test is the LAL assay, and results are given in endotoxin units. Endotoxin is a separate question from sterility. A sample can hold no living organisms at all and still carry endotoxin left by bacteria that were killed earlier.
Does “research grade” mean anything?
Ideally it means there is paperwork behind the material. Identity is confirmed, purity is measured, results are linked to one lot, and the product is sold for lab use only. But no regulator defines the term, so on its own it promises nothing. The documents give it meaning. The label does not.
How can you check a purity claim yourself?
Start by matching paper to vial. The lot number on the label has to appear on the certificate. Next, confirm the certificate names an independent lab. It should report an HPLC purity figure and an identity result, from mass spectrometry or from HPLC against a reference standard. It should also show a test date. If any of these is absent, treat the figure as unverified.