Account chemist periodically culled for vanity (7)
I believe the answer is:
conceit
'for vanity' is the definition.
(synonyms)
'account chemist periodically' is the wordplay.
'periodically' means one should take alternating letters (letters must be selected 'every so often').
'account'+'chemist'='accountchemist'
The alternating letters of 'accountchemist' are 'CONCEIT'.
'culled' is the link.
I am not very happy about this link. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for conceit that I've seen before include "Fanciful notion; excessive pride in oneself" , "Self-importance - idea" , "Fanciful notion; self-pride" , "Vanity; fanciful notion" , "Overbearing self-esteem" .)