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: Mesna ' s action , in conjunction with IFO reduces the frequency of SCEs , in comparison with the SCEs recordings obtained when IFO is administered alone .
### Output Text:
<span class="chemical">Mesna</span> ' s action , in conjunction with <span class="chemical">IFO</span> reduces the frequency of SCEs , in comparison with the SCEs recordings obtained when <span class="chemical">IFO</span> is administered alone . 