I'm unadulterated, not dirty (6)

I believe the answer is:

impure

I'm a little stuck... Click here to teach me more about this clue!

'not dirty' is the definition.
'impure' can be an answer for 'dirty' (I've seen this before). I am unsure of the 'not' bit.

'i'm unadulterated' is the wordplay.
'unadulterated' becomes 'pure' (similar in meaning).
'im'+'pure'='IMPURE'

Can you help me to learn more?

(Other definitions for impure that I've seen before include "Assign a value to" , "Dirty or immoral" , "Unrefined" , "Adulterated or unchaste" , "Sullied or adulterated" .)

I've seen this clue in the Evening Standard.

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