feed

https://doi.org/10.1351/goldbook.10177
Solution or gas containing analyte introduced into an extraction.
Note: If feed is used without qualification, the term may be taken to designate the initial liquid phase containing the main solute to be transferred or sample solution in a batch process.
Source:
PAC, 2016, 88, 517. (Glossary of terms used in extraction (IUPAC Recommendations 2016)) on page 523 [Terms] [Paper]