A term describing the co-operative effect of two (or more) extractants where the distribution ratio for the combination is greater than the largest individual distribution ratio (measured under comparable conditions).
The corresponding adjective is synergic and the term synergistic should not be used.
No standard method for quantification of the phenomenon has been agreed and any approach should be clearly defined in a given situation.
PAC, 1993, 65, 2373
(Nomenclature for liquid-liquid distribution (solvent extraction) (IUPAC Recommendations 1993))
on page 2379
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. doi:10.1351/goldbook