What Does a Peptide HPLC Chromatogram Show?

An HPLC chromatogram is a two-axis plot that shows what came off a chromatography column and when. The horizontal axis is retention time in minutes, measured from the moment the sample is loaded onto the column. The vertical axis is UV absorbance, usually at 214 nm, in milliabsorbance units (mAU) [1]. Each compound in the sample appears as a peak at a characteristic retention time, and the area under each peak reflects its relative abundance.

What does the main peak represent?

The tallest peak, if the sample is reasonably pure, is the target peptide. The percentage of total peak area that belongs to this peak is the HPLC purity. A sample reported as 98 percent pure means 98 percent of the UV-absorbing material in the run was in the main peak.

What do the smaller peaks mean?

Smaller peaks represent impurities: deletion sequences, oxidized variants, deamidated forms, truncated sequences, or residual protecting groups left from synthesis [2]. Their retention times relative to the main peak sometimes reveal their identity. An oxidized peptide, for example, is slightly more polar and typically elutes a few seconds before the parent.

What artifacts should be watched for?

A sloping baseline suggests the column was not equilibrated. A tailing peak, with a drawn-out right side, may indicate column overloading or a secondary interaction with the stationary phase. A shoulder on the main peak suggests a co-eluting impurity that is not fully resolved, which inflates the apparent purity.

Frequently asked questions

Can two different peptides give the same retention time?

Yes. Retention time depends on polarity, not identity. Mass spectrometry is needed to confirm what a peak actually is.

Why is 214 nm the standard wavelength?

Because the peptide bond (the amide linkage between amino acids) absorbs UV light most strongly near 214 nm, making it a universal detector for peptides.