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: RESULTS : Unexpectedly high concentrations of argatroban were measured in these samples ( range , 0 - 32 microg / mL ) , and a prolonged plasma argatroban half life ( t ( 1 / 2 ) ) of 514 minutes was observed ( published elimination t ( 1 / 2 ) is 39 - 51 minutes [ < or = 181 minutes with hepatic impairment ] ) .
### Output Text:
RESULTS : Unexpectedly high concentrations of <span class="chemical">argatroban</span> were measured in these samples ( range , 0 - 32 microg / mL ) , and a prolonged plasma <span class="chemical">argatroban</span> half life ( t ( 1 / 2 ) ) of 514 minutes was observed ( published elimination t ( 1 / 2 ) is 39 - 51 minutes [ < or = 181 minutes with hepatic impairment ] ) . 