group preconcentration

in trace analysis
https://doi.org/10.1351/goldbook.G02707
An operation (process) as a result of which several microcomponents are isolated in one step. This may be achieved in one of two ways, by transportation either of the matrix or of the microcomponents into a second phase. The first method is widely used in the analysis of relatively simple substances and materials.
Source:
PAC, 1979, 51, 1195. (Separation and Preconcentration of Trace Substances. I-Preconcentration for Inorganic Trace Analysis) on page 1198 [Terms] [Paper]