What a purity percentage measures
In HPLC (high-performance liquid chromatography) the sample is pushed through a column. Different molecules come out at different times and a detector draws a peak for each. The target peptide should be one tall peak. Anything else shows up as smaller peaks.
Purity is normally reported as area percent: the main peak's area divided by the area of all detected peaks. A result of 99.97% means 99.97% of the detected signal came from the main peak.
What it does not tell you: whether the main peak is the right compound, how much powder is in the vial, or whether there is anything the detector cannot see, such as water, salts or endotoxin.
HPLC vs mass spectrometry
- HPLC answers "how pure?" It separates and measures peaks but cannot by itself name what each peak is.
- Mass spectrometry answers "what is it?" It measures molecular mass, which confirms identity. LC-MS combines both in one run.
- Content or net content answers "how much?" Labs such as Janoshik report mg per vial; North American Diagnostics calls it mass content; Freedom Diagnostics lists net content as its own test.
Why two "99%" claims are not the same
- Lot result vs blanket claim. A number tied to a batch and a test ID is a measurement. A site-wide "99%+" is a promise.
- Area % vs mass %. Janoshik offers an alternative m/m (mass by mass) purity format. Area percent and mass percent can give different numbers for the same vial.
- Different pass marks. Finnrick grades purity against thresholds from 98% to 99.8% depending on the standard selected. The same vial can pass one and fail another.
- What was left out. Counter-ions such as TFA are not part of a standard purity result. Janoshik lists TFA analysis as a separate add-on.
- Who chose the sample. A vendor-submitted vial and a store-bought vial answer different questions.
Purity claims as vendors publish them
Copied from vendor pages and lab lookups on Nov 6, 2026.