Understanding Purity: What ≥98% Really Tells You
A purity figure looks simple, but reading it well means knowing what it measures, what it doesn't, and why the method behind the number matters as much as the number itself.
By LOCKED Research Team · Analytical Standards
Research Use Only. This article is educational and does not constitute medical advice or a claim of safety or efficacy. LOCKED products are supplied for laboratory research use only (RUO). They are not drugs, foods, dietary supplements, cosmetics, or medical devices, are not for human or animal consumption, and are not intended to diagnose, treat, cure, or prevent any disease. LOCKED makes no medical, therapeutic, or performance claims. The purchaser is solely responsible for compliance with all applicable laws and for lawful use.
"≥98% purity" is one of the most quoted figures in research supply — and one of the most misunderstood. Reading it correctly is a small skill with a large payoff.
What the number measures
Purity, as reported on a Certificate of Analysis, is the proportion of the sample that is the target compound, with the remainder being impurities — typically process-related by-products. When purity is measured by reversed-phase HPLC, the figure comes from the relative area of the main peak against everything else in the chromatogram. "≥98%" means the target compound accounts for at least 98% of the resolved material.
What the number does not measure
A purity percentage does not, on its own, tell you the identity of the main peak — that is a separate question answered by mass spectrometry. Nor does it describe the nature of the remaining 2%. Two materials can share a purity figure and differ in their impurity profiles. This is why a complete analytical package pairs the purity figure with an identity confirmation and, ideally, the chromatogram itself.
Why the method matters
A number without a method is not a measurement. "98% pure" means something specific when tied to RP-HPLC with a stated gradient; it means very little as a bare marketing phrase. When you evaluate a purity claim, look for the method name and, where available, the chromatogram behind it.
A range is a warning sign
Reputable certificates report purity as a single figure for a specific batch — not a range like "95–99%." A range usually means the number describes a product line's typical performance, not the actual material in your vial. Batch-specific means the figure was measured on that batch.
The practical takeaway
When you read "≥98%," ask three questions: measured by what method, confirmed as which compound, and on which specific batch? A certificate that answers all three has earned the number. LOCKED reports purity per batch, by RP-HPLC, alongside mass-spec identity — so the figure is a measurement, not a slogan.