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: Both treatments significantly reduced DPI by the 30th minute ( GTN , - 12 . 8 + / - 17 . 9 ; DCF , - 18 . 9 + / - 16 . 6 ) .
### Output Text:
Both treatments significantly reduced DPI by the 30th minute ( <span class="chemical">GTN</span> , - 12 . 8 + / - 17 . 9 ; <span class="chemical">DCF</span> , - 18 . 9 + / - 16 . 6 ) . 