Sickened when sodium application ruined date (9)
I believe the answer is:
nauseated
'sickened' is the definition.
('nauseate' can be a synonym of 'sicken')
'sodium application ruined date' is the wordplay.
'sodium' becomes 'NA' (chemical symbol).
'application' becomes 'use' (I've seen this in other clues).
'ruined' indicates anagramming the letters.
'date' is an anagram of 'ated'.
'na'+'use'+'ated'='NAUSEATED'
'when' acts as a link.
(Other definitions for nauseated that I've seen before include "Disgusted" , "Sickened" , "Revolted" .)