Most deep groundwater does not need screening before other purification steps.

For natural proteins, a series of purification steps may be necessary to obtain protein sufficiently pure for laboratory applications.

A purification step is necessary to remove contaminating substances.

These large particles can cause a phenomenon called membrane fouling in later purification steps.

Further purification steps are required to produce usable metallic scandium.

(These empty reactions are gotten rid of by the purification step described in the last paragraph.)

In many cases, the product can simply be filtered from the solution as the only purification step required.

All purification steps contained dithiothreitol to prevent oxidation of the proteins.

The purification steps are summarized in Table 4.

An extra intermediate purification step can be added or optimization of the different steps is performed for improving purity.