When contamination is ruled out, turbidity in cell culture media is often explained by the precipitation of metals, proteins, and other media components. Precipitates can be harmful to cell health, as they may alter media composition by removing nutrients and other desirable components by processes such as chelation. Precipitates are also visible by microscopy as artifact, and may therefore interfere with assays that rely on imaging.
Purposeful precipitaton. Although precipitates are generally undesirable in cell culture, precipitation may be exploited as a purification strategy for proteins in the supernatant. For example, ammonium sulfate precipitation is used to purify antibodies from hybridoma supernatant or serum in a technique sometimes referred to as ‘salting out’.