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: Hyponatremia and syndrome of inappropriate anti - diuretic hormone reported with the use of Vincristine : an over - representation of Asians ?
### Output Text:
Hyponatremia and syndrome of inappropriate anti - diuretic hormone reported with the use of <span class="chemical">Vincristine</span> : an over - representation of Asians ? 