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: Two hr post - injection , DXNP was 2 . 7 times more concentrated in kidneys than free DX ( p < 0 . 025 ) .
### Output Text:
Two hr post - injection , DXNP was 2 . 7 times more concentrated in kidneys than free <span class="chemical">DX</span> ( p < 0 . 025 ) . 