In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: A higher residual serum concentration of temazepam correlated with a lower MMSE sum score after adjustment for confounding variables .
### Output Text:
A higher residual serum concentration of <span class="chemical">temazepam</span> correlated with a lower MMSE sum score after adjustment for confounding variables . 