High-performance liquid chromatography (HPLC) is the workhorse method for measuring peptide purity. Every certificate in our library includes an HPLC result — here is how to read it.
The chromatogram
The sample is pushed through a column that separates its components. A detector records each one as a peak over time. A pure sample shows one dominant peak; impurities appear as smaller peaks before or after it.
Retention time
Retention time is when the main peak appears. It is characteristic of the compound under a given method and helps confirm that the right molecule was measured.
Purity percentage
Purity is the area of the main peak as a percentage of the total peak area. A result of 99.2% means impurities make up less than 1% of what the detector measured.
What HPLC does not tell you
HPLC measures relative purity, not identity. That is why every batch is also analysed by mass spectrometry, which confirms that the main peak has the expected molecular weight.
