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: Plasma sodium concentrations were found to be slightly increased in the Li - treated rats compared with those in controls .
### Output Text:
Plasma <span class="chemical">sodium</span> concentrations were found to be slightly increased in the <span class="chemical">Li</span> - treated rats compared with those in controls . 