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: To determine whether there was a temporal relationship between VPA - associated oxidative stress and hepatotoxicity , adult male Sprague - Dawley rats were treated ip with VPA ( 500 mg / kg ) or 0 . 9 % saline ( vehicle ) once daily for 2 , 4 , 7 , 10 , or 14 days .
### Output Text:
To determine whether there was a temporal relationship between <span class="chemical">VPA</span> - associated oxidative stress and hepatotoxicity , adult male Sprague - Dawley rats were treated ip with <span class="chemical">VPA</span> ( 500 mg / kg ) or 0 . 9 % saline ( vehicle ) once daily for 2 , 4 , 7 , 10 , or 14 days . 