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: Argatroban prolongs the International Normalized Ratio , and published approaches for monitoring the argatroban - to - warfarin transition should be followed .
### Output Text:
<span class="chemical">Argatroban</span> prolongs the International Normalized Ratio , and published approaches for monitoring the <span class="chemical">argatroban</span> - to - <span class="chemical">warfarin</span> transition should be followed . 