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: Furthermore , data obtained with phentolamine alone do not suggest alpha - adrenoceptor desensitization as the cause of the enhanced neurotransmitter overflow after epinephrine treatment .
### Output Text:
Furthermore , data obtained with <span class="chemical">phentolamine</span> alone do not suggest alpha - adrenoceptor desensitization as the cause of the enhanced neurotransmitter overflow after <span class="chemical">epinephrine</span> treatment . 