Why might an analyte need a carrier species for complete precipitation?

In analytical chemistry, the complete precipitation of an analyte may be difficult to achieve if the analyte is present in very low concentrations or forms a precipitate that is too finely divided to be easily filtered. To address this, a carrier species is added to the solution to "co-precipitate" with the analyte under the same reaction conditions.1

The carrier acts as a host or support, ensuring that the analyte is effectively removed from the solution along with the carrier material. When selecting a carrier, it is essential to choose a substance that will not interfere with subsequent analytical manipulations of the analyte.1

While carriers are useful for ensuring complete recovery, analysts must be cautious of unintended co-precipitation, where an interferent from the sample matrix is inadvertently captured alongside the analyte. In such instances, specific chemical strategies must be employed to prevent the inclusion of these unwanted contaminants.1