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 serum K during the control period was 4 . 5 + / - 0 . 2 mEq / l an on 50 , 100 , 150 and 200 mg HCTZ daily 3 . 9 + / - 0 . 3 , 3 . 4 + / - 0 . 2 , 2 . 9 + / - 0 . 2 , and 2 . 4 + / - 0 . 3 mEq / l , respectively .
### Output Text:
The serum <span class="chemical">K</span> during the control period was 4 . 5 + / - 0 . 2 mEq / l an on 50 , 100 , 150 and 200 mg <span class="chemical">HCTZ</span> daily 3 . 9 + / - 0 . 3 , 3 . 4 + / - 0 . 2 , 2 . 9 + / - 0 . 2 , and 2 . 4 + / - 0 . 3 mEq / l , respectively . 