Before the first chromatography step it is necessary to remove unbroken cells, lipids, and particulate matter from the protein solution.
For some applications it is sufficient to use a low centrifugation step: 15 min at 10,000 g (e.g. 15,000 rpm using a Sorvall SS-34 rotor).
When a very clear sample is needed, e.g. for refolding or when the sample is directly applied to an expensive chromatography column, an ultracentrifugation step becomes necessary: 30 min at >100,000 g (45,000 rpm using a Beckman 45Ti rotor).