In sedimentation equilibrium centrifugation
(or density gradient centrifugation),
different molecules in the mixture will settle in bands of different buoyant densities where
the centrifugal force is equal and opposite to the upward diffusion force.
The gradient is eluted from the tube in fractions, which can then be measured for UV absorption at 260 nm.
This technique can be used to analyze base composition of double-stranded DNA.