Variations in chemical make-up established by organisation that standardises drinks (8)
I believe the answer is:
isotopes
'variations in chemical make-up' is the definition.
Although both the answer and definition are plural nouns, I can't see how one could define the other.
'organisation that standardises drinks' is the wordplay.
I cannot really see how this works, but
'organisation' could be 'iso' (I've seen this in another clue) and 'iso' is present in the answer.
'drinks' could be 'topes' ('tope' can be a synonym of 'drink') and 'topes' is present in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'established by' acts as a link.
Can you help me to learn more?
(Other definitions for isotopes that I've seen before include "Stoops, i.e. to become odd types of atoms" , "what may be used for diagnostic purposes" , "atomic elements" , "Poet is so confused about forms of chemical elements" , "Variant forms of element" .)