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: Although the United States Food and Drug Administration banned its use for nocturnal leg cramps due to lack of safety and efficacy , quinine is widely available in beverages including tonic water and bitter lemon .
### Output Text:
Although the United States Food and Drug Administration banned its use for nocturnal leg cramps due to lack of safety and efficacy , <span class="chemical">quinine</span> is widely available in beverages including tonic water and bitter lemon . 