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: L - arginine uptake was assessed in mononuclear cells incubated with L - arginine ( 1 to 300 micromol / L ) , incorporating 100 nmol / L [ 3H ] - l - arginine for a period of 5 minutes at 37 degrees C .
### Output Text:
<span class="chemical">L - arginine</span> uptake was assessed in mononuclear cells incubated with <span class="chemical">L - arginine</span> ( 1 to 300 micromol / L ) , incorporating 100 nmol / L <span class="chemical">[ 3H ] - l - arginine</span> for a period of 5 minutes at 37 degrees C . 