Fig. 3From: Reconciling differences pertaining to the origin of SARS-CoV-2Purification of virions by density gradient centrifugation. A partly purified preparation of virus is further purified in a density gradient. Rate zonal centrifugation involves layering the preparation on top of a pre-formed gradient. Equilibrium centrifugation can often be done starting with a suspension of the impure virus in a solution of the gradient material; the gradient is formed during centrifugation (Carter and Saunders 2007)Back to article page