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: In 25 out of 32 episodes ( 78 % ) , plasma ammonium levels and mental status returned to normal within 2 days after adequate management .
### Output Text:
In 25 out of 32 episodes ( 78 % ) , plasma <span class="chemical">ammonium</span> levels and mental status returned to normal within 2 days after adequate management . 