How it works
Purity is read from a chromatogram as area percent: the target peak’s area divided by the summed area of all integrated peaks. It is an arithmetic ratio of what the method resolved, not an absolute count of everything present.
Because it depends on the separation, purity is method-dependent. The column, the gradient, and the detection wavelength all shape which impurities are resolved and counted, so two labs’ “98%” on different methods are not necessarily the same claim.
It measures relative composition, not identity. A sample can be highly pure and still be the wrong compound; purity answers “how much of this is the target,” while identity — answered by ESI-MS — answers “is the target what I think it is.”
Why it matters
Purity underpins release decisions, batch comparison, and stability monitoring, because it condenses composition into one comparable figure — provided the method is held constant.
Its method-dependence is the reason a certificate states the method, not just the result: a purity number without its method cannot be compared honestly.
Read with its limits, purity is powerful; read as an absolute, it misleads. Anything that co-elutes with the target or does not absorb at the detection wavelength is not counted, so the trace matters as much as the number.
Purity answers how much of this is the target; identity answers whether the target is what you think it is.
At Lineará
Purity by RP-HPLC is the headline analytical result on every certificate, reported as a percentage alongside the method used to measure it.
Because purity is a property of a lot, it is reported per lot; comparing certificates across lots is how stability over time becomes visible.