Chromatography Practice Test

Which statement about gradient elution is false?

Gradient elution uses a mobile phase composition that changes during the run.

Gradient elution often requires re-equilibration between runs.

Gradient elution can improve separation of closely eluting compounds.

Gradient elution eliminates the need to re-equilibrate the column after each run.

Gradient elution changes the mobile phase composition during the run, which lets you tailor the elution strength to separate compounds with a wide range of polarities and can speed up analysis. Because the column ends up with a different mobile phase after a gradient, you typically need to re-equilibrate it back to the starting conditions before the next run to ensure consistent retention times and peak shapes. So the statement that gradient elution eliminates the need to re-equilibrate is not correct. In contrast, gradient elution can indeed improve the separation of closely eluting compounds by gradually adjusting the elution strength, aiding resolution. It also often requires re-equilibration between runs to restore the initial conditions.