How HPLC and Mass Spectrometry Verify Purity
Analytical methods reference · research use only
Every purity figure on a Certificate of Analysis comes from an instrument, and two instruments do almost all of the work: reverse-phase HPLC answers "how much of this is the target compound", and mass spectrometry answers "is this the right compound at all". Neither answers the other's question.
Reverse-phase HPLC — the purity number
In reverse-phase high-performance liquid chromatography, the sample is carried in a solvent gradient through a column packed with a non-polar stationary phase. Peptides adsorb to that phase and release as the solvent becomes less polar, so components emerge separated in time. A detector records each as a peak.
Purity is then an area calculation: the target peak's area as a percentage of total peak area. A result of ≥99.2% means that under the stated method, no more than 0.8% of detected material was anything other than the target. Two points follow from that definition, and both matter when reading a COA: the figure is method-dependent, and it describes what the detector could see.
Mass spectrometry — the identity confirmation
Mass spectrometry ionises the sample and measures mass-to-charge ratio, yielding the molecular weight of what is actually present. Compared against the theoretical mass computed from the sequence, this is what confirms identity rather than mere purity. For closely related pairs the resolution matters enormously — MT-II and PT-141 differ by roughly one mass unit, which is exactly the case high-resolution instruments exist to resolve.
Why both, and why independent
A sample can be 99.9% pure and be the wrong molecule. It can also be the right molecule at 80% purity. Only running both analyses closes both questions. Glow Peptides releases each lot against testing performed by an independent U.S. laboratory rather than in-house figures, and the resulting report is lot-specific — tied to the exact material in the vial, not to the compound in general.
To read one of these reports line by line, see how to read a Certificate of Analysis.
Supplied strictly as a research reference material for in-vitro laboratory use. Not for human or veterinary use.
Frequently asked questions
What does a ≥99.2% HPLC purity result actually mean?
Under the stated chromatographic method, the target compound accounted for at least 99.2% of total detected peak area — meaning no more than 0.8% of detected material was anything else. The figure is method-dependent and describes what the detector could see.
Why is mass spectrometry needed if HPLC already gives a purity number?
HPLC quantifies how much of the sample is the main component; it does not prove which molecule that component is. Mass spectrometry measures molecular weight and confirms identity against the theoretical mass. Both analyses are required to answer both questions.
Does a Certificate of Analysis apply to every vial of that compound?
No. A COA is lot-specific. It documents the material in that production lot, which is why the lot number on the vial should match the report.