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: Deep forearm venous samples were collected for determination of L - arginine extraction .
### Output Text:
Deep forearm venous samples were collected for determination of <span class="chemical">L - arginine</span> extraction . 