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: Patients ' , who had hepatotoxicity on sulfasalazine and met a definition of a serious ADR , were identified .
### Output Text:
Patients ' , who had hepatotoxicity on <span class="chemical">sulfasalazine</span> and met a definition of a serious ADR , were identified . 