HPLC
In short High-performance liquid chromatography, a separation method used to measure peptide purity.
In HPLC a small amount of the dissolved sample is pumped under high pressure through a column packed with fine particles. Different components of the sample interact with the packing to different degrees, so they leave the column at different times. A detector, usually ultraviolet absorbance, records each one as a peak.
For peptides the usual form is reversed-phase HPLC, in which more hydrophobic molecules are held back longer. The area of the main peak relative to the total area of all peaks gives the purity figure on the certificate. Closely related impurities, such as a peptide missing one residue, often appear as small peaks next to the main one.
UPLC is the same principle with smaller particles and higher pressure, giving sharper peaks and faster runs. HPLC tells you how much of the sample is one component; it does not by itself prove which molecule that component is. That is why it is often paired with mass spectrometry.
APIGENEX s.r.o., one of the two laboratories in our certificate library, reports HPLC or UPLC purity.