extraction phase

https://doi.org/10.1351/goldbook.10175
Liquid, solid, or gas phase in contact with the sample for the purpose of removal of analytes from the sample matrix.
Source:
PAC, 2016, 88, 517. 'Glossary of terms used in extraction (IUPAC Recommendations 2016)' on page 523 (https://doi.org/10.1515/pac-2015-0903)