Sample of zinc has tested 'pure (6)
I believe the answer is:
chaste
''pure' is the definition.
(chaste means abstaining from sex)
'sample of zinc has tested' is the wordplay.
'sample of' says the answer is hidden in the clue (an extract or sample of the clue).
'CHASTE' is hidden in the letters of 'zinc has tested'.
(Other definitions for chaste that I've seen before include "Pure and decent" , "Like Diana" , "Innocent" , "Sachet (anag)" , "Modest, pure" .)