Take advantage of carbon used with advanced body part (4,2)
I believe the answer is:
cash in
'take advantage of' is the definition.
(I've seen this before)
'carbon used with advanced body part' is the wordplay.
'carbon' becomes 'C' (chemical symbol).
'used with' is a charade indicator (letters next to each other).
'advanced' becomes 'a' (abbreviation).
'body part' becomes 'shin' (shin is a kind of body part).
'c'+'a'+'shin'='CASH IN'
(Other definitions for cash in that I've seen before include "Take advantage of" , "Make money" , "Exchange for money; seize an advantage" , "Realise" , "Get ready" .)