Peak Impurities Revealed

Shown here is a chromatogram obtained under isocratic conditions. It appears to be a simple three component mixture.

Purity checks were made with ultra fast “on-the-fly” scans on the ascending and descending sides of each peak. Peaks 1 and 2 gave identical spectral scans on each side, but peak 3 gave totally different spectra from its two sides indicating a major impurity producing the scan shown in red. Scans were compared by normalising and overlaying.

Despite the impurity, peak 3 appears visually symmetric and it’s calculated asymmetry factor was
close to 1.00.