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 nitrate / nitrite ( NOx ) was decreased in dex - treated rats compared to saline - treated rats ( 11 . 2 + / - 1 . 08 microm , 15 . 3 + / - 1 . 17 microm , respectively , P < 0 . 05 ) .
### Output Text:
Plasma <span class="chemical">nitrate</span> / <span class="chemical">nitrite</span> ( NOx ) was decreased in <span class="chemical">dex</span> - treated rats compared to saline - treated rats ( 11 . 2 + / - 1 . 08 microm , 15 . 3 + / - 1 . 17 microm , respectively , P < 0 . 05 ) . 