Restrict distribution of nitrates (8)
I believe the answer is:
straiten
'restrict' is the definition.
(I've seen this before)
'distribution of nitrates' is the wordplay.
'distribution of' indicates anagramming the letters.
'nitrates' anagrammed gives 'STRAITEN'.
(Other definitions for straiten that I've seen before include "Train set (anag.)" , "Restrict" , "distress" , "Limit" .)