Understanding peptide purity: what 99% means

Purity percentage is the most quoted and least understood figure. A solid 99% and an unbacked 99% are not worth the same, and here is why.

What HPLC purity actually measures

High-performance liquid chromatography (HPLC) separates the sample's components and measures what proportion is the target peptide versus impurities, fragments or synthesis by-products. 99% means 99% of the integrated peak is the correct compound.

Purity is not the same as identity

HPLC tells you how much of the compound is there; mass spectrometry confirms that compound is actually what it claims to be. A serious CoA includes both: purity (HPLC) and identity (MS). Without confirmed identity, a high purity may be measuring the wrong peptide.

Why test rigour changes the value of the number

A 99.7% verified by an independent lab, checkable on its own domain and recently dated, is robust data. The same 99.7% in a PDF with no verifiable lab, or a year old, is far weaker: you don't know whether it matches the vial you receive. That is why we weight purity by the rigour of the analysis.

What range is genuinely good

For research peptides, 99%+ is excellent, 98-99% is solid, 95-98% is acceptable depending on the compound, and below 95% you should ask questions. But the number only matters if the test behind it is verifiable and recent.