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: However , we experienced a case of severe ocular and orbital toxicity after intracarotid injection of carboplatin , which is infrequently reported .
### Output Text:
However , we experienced a case of severe ocular and orbital toxicity after intracarotid injection of <span class="chemical">carboplatin</span> , which is infrequently reported . 