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: The effect of L - dopa was correlated with a decrease in blood and brain ammonia , an increase in brain dopamine , and an increase in renal excretion of ammonia and urea .
### Output Text:
The effect of <span class="chemical">L - dopa</span> was correlated with a decrease in blood and brain <span class="chemical">ammonia</span> , an increase in brain <span class="chemical">dopamine</span> , and an increase in renal excretion of <span class="chemical">ammonia</span> and <span class="chemical">urea</span> . 