Continuous optical interrogation of a packed-sorbent bed in a flow system at any stage of the extraction process prior to analyte elution and sorbent regeneration.
Source: PAC, 2016, 88, 517. 'Glossary of terms used in extraction (IUPAC Recommendations 2016)' on page 554 (https://doi.org/10.1515/pac-2015-0903)