Contemptuously replacing nitrogen with chlorine at regular intervals (10)

I believe the answer is:

cyclically

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

'at regular intervals' is the definition.

'contemptuously replacing nitrogen with chlorine' is the wordplay.
I cannot quite understand how this works, but
'chlorine' could be 'cl' (chemical symbol) and 'cl' is found within the answer.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?

I've seen this clue in The Guardian.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.