preconcentration coefficient 

of a desired microcomponent, in trace analysis
https://doi.org/10.1351/goldbook.P04804
This is defined as K=QT/QMQTo/QMo where QT and QTo are the quantities of the microcomponent in the concentrate and in the sample, respectively (mass units or concentration units), and QMo and QM and are the quantities of the matrix before and after preconcentration, respectively. If the recovery is 100%, K=QMoQM. The terms enrichment coefficient and enrichment factor are not recommended.
Source:
PAC, 1979, 51, 1195. (Separation and Preconcentration of Trace Substances. I-Preconcentration for Inorganic Trace Analysis) on page 1198 [Terms] [Paper]