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: We investigate whether abnormalities in L - arginine uptake contribute to this deficiency .
### Output Text:
We investigate whether abnormalities in <span class="chemical">L - arginine</span> uptake contribute to this deficiency . 