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: Long - term intragastric application of the antiepileptic drug sodium valproate ( Vupral " Polfa " ) at the effective dose of 200 mg / kg b .
### Output Text:
Long - term intragastric application of the antiepileptic drug <span class="chemical">sodium valproate</span> ( Vupral " Polfa " ) at the effective dose of 200 mg / kg b . 