Concentrate of spun copper sulphate, primarily (5)
I believe the answer is:
focus
'concentrate' is the definition.
(I know that concentrate can be written as focus)
'of spun copper sulphate primarily' is the wordplay.
'spun' is a reversal indicator.
'copper' becomes 'Cu' (chemical symbol).
'primarily' says to take the initial letters.
The initial letter of 'sulphate' is 's'.
'of' backwards is 'fo'.
'fo'+'cu'+'s'='FOCUS'
(Other definitions for focus that I've seen before include "Hub" , "Concentrate, centre attention" , "Concentrate on something, perhaps with camera" , "Central point" , "Where light-rays meet" .)