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: Symptomatic hypokalemia has been reported in such patients ( 3 - 7 ) and in one case hypocalcemia was observed ( 8 ) , but the effects of magnesium depletion were not noted in these patients .
### Output Text:
Symptomatic hypokalemia has been reported in such patients ( 3 - 7 ) and in one case hypocalcemia was observed ( 8 ) , but the effects of <span class="chemical">magnesium</span> depletion were not noted in these patients . 