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''Product isolation'' is the removal of those components whose properties vary markedly from that of the desired product. For most products, water is the chief impurity and isolation steps are designed to remove most of it, reducing the volume of material to be handled and concentrating the product. [[Solvent]] extraction, [[adsorption]], ultrafiltration, and [[Precipitation (chemistry)|precipitation]] are some of the unit operations involved.
''Product purification'' is done to separate those contaminants that resemble the product very closely in physical and chemical properties. Consequently steps in this stage are expensive to carry out and require sensitive and sophisticated equipment. This stage contributes a significant fraction of the entire downstream processing expenditure. Examples of operations include affinity, size exclusion, reversed phase [[chromatography]], [[Ion chromatography|ion-exchange chromatography]], [[crystallization]] and fractional precipitation.
''Product polishing'' describes the final processing steps which end with packaging of the product in a form that is stable, easily transportable and convenient. [[Crystallization]], [[desiccation]], [[lyophilization]] and spray drying are typical unit operations. Depending on the product and its intended use, polishing may also include operations to sterilize the product and remove or deactivate trace contaminants which might compromise product safety. Such operations might include the [[Viral processing|removal of viruses]] or [[depyrogenation]].
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