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: Here , we describe the case of a 15 - year - old girl who was on a long - term therapy with valproate due to epilepsy and revealed impaired consciousness with hyperammonemia 12 days after renal transplantation .
### Output Text:
Here , we describe the case of a 15 - year - old girl who was on a long - term therapy with <span class="chemical">valproate</span> due to epilepsy and revealed impaired consciousness with hyperammonemia 12 days after renal transplantation . 