Chromatogram
A chromatogram is the plot a chromatography run produces, showing detector signal against retention time, with each separated component appearing as a peak.
Time runs along the horizontal axis, usually in minutes from the start of the run, and the detector's signal runs up the vertical one, in milli-absorbance (mAU) for a UV detector. Each component that leaves the column draws a peak. Its retention time helps tell components apart, and the area under it reflects how much of that component there is. The integration table printed with a chromatogram lists each peak's time and area, and purity is the main peak's share of the total.
A clean main peak rises from a flat baseline and returns to it. A shoulder on its side, or a long tail, can mean an impurity leaving the column with the compound. Small peaks should appear in the table if they were counted; a table listing a single peak may only reflect where the analyst set the integration threshold. The purity on the certificate should match the main peak's area percentage in the table.
A chromatogram adds what a bare purity figure cannot: it shows how the number was reached. It still cannot establish identity. A retention time means something only against a reference standard run under the same conditions, and the plot shows only what the detector responds to, so water, salts and counter-ions are invisible on it.
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UPDATED OCTOBER 30, 2026 · REVIEWED BY DEL POTTER, PHD