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 , peripheral blood monocytes isolated from ritonavir - treated females had less cholesteryl ester accumulation .
### Output Text:
Furthermore , peripheral blood monocytes isolated from <span class="chemical">ritonavir</span> - treated females had less <span class="chemical">cholesteryl ester</span> accumulation . 