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: An experiment was performed to test whether inclusion of phenobarbital in a choline - devoid diet would increase the hepatocarcinogenicity of the diet .
### Output Text:
An experiment was performed to test whether inclusion of <span class="chemical">phenobarbital</span> in a <span class="chemical">choline</span> - devoid diet would increase the hepatocarcinogenicity of the diet . 