solvent

in liquid-liquid distribution
The term applied to the whole initial liquid phase containing the extractant.
Notes:
  1. The solvent may contain only one extractant or it may be a composite homogeneous mixture of extractant(s) with diluent(s) and also sometimes modifiers and accelerators.
  2. The term solvent must not be used as a synonym for any of the individual components of a composite liquid phase even where, in the case of a single component (e.g. 3-methylbutan-2-one or tributyl phosphate), it becomes identical with the extractant.
  3. The term may be qualified to denote the extract from a given processing step e.g. loaded solvent.
Source:
PAC, 1993, 65, 2373 (Nomenclature for liquid-liquid distribution (solvent extraction) (IUPAC Recommendations 1993)) on page 2381