Separate after carbon copy (5)
I believe the answer is:
clone
'copy' is the definition.
(I've seen this before)
'separate after carbon' is the wordplay.
'separate' becomes 'lone' ('lone' can be a synonym of 'separate').
'after' means one lot of letters go next to another.
'carbon' becomes 'c' (C is the chemical symbol for carbon).
'lone' after 'c' is 'CLONE'.
(Other definitions for clone that I've seen before include "Person who is identical to another" , "Exact replica" , "Biological replica" , "Genetic double" , "Not an original individual" .)