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 - Dopa intake was found to cause an increased excretion of potassium , and sometimes also of sodium , in the hypokalemic but not in the normokalemic patients .
### Output Text:
<span class="chemical">L - Dopa</span> intake was found to cause an increased excretion of <span class="chemical">potassium</span> , and sometimes also of <span class="chemical">sodium</span> , in the hypokalemic but not in the normokalemic patients . 