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 : Serum sFas was significantly increased in patients with acute liver failure ( median , 26 . 8 U / mL ; range , 6 . 9 - 52 . 7 U / mL ) compared to the normal controls ( median , 8 . 6 U / mL ; range , 6 . 5 - 12 . 0 U / mL , P < 0 . 0001 ) .
### Output Text:
RESULTS : Serum sFas was significantly increased in patients with acute liver failure ( median , 26 . 8 U / mL ; range , 6 . 9 - 52 . 7 U / mL ) compared to the normal controls ( median , 8 . 6 U / mL ; range , 6 . 5 - 12 . 0 U / mL , P < 0 . 0001 ) . 