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: It was concluded that formulations at or below 0 . 5 per cent CHP may prove acceptable for wound care , but the vehicle system needs pharmaceutical improvement to render it more tolerable and easier to use .
### Output Text:
It was concluded that formulations at or below 0 . 5 per cent <span class="chemical">CHP</span> may prove acceptable for wound care , but the vehicle system needs pharmaceutical improvement to render it more tolerable and easier to use . 