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: Fourteen of 39 dialysis patients ( 36 % ) became hypercalcemic after switching to calcium carbonate as their principal phosphate binder .
### Output Text:
Fourteen of 39 dialysis patients ( 36 % ) became hypercalcemic after switching to <span class="chemical">calcium carbonate</span> as their principal <span class="chemical">phosphate</span> binder . 