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: METHODS : This randomized , double - blinded study was conducted in 100 patients randomly allocated into five groups of 20 patients each .
### Output Text:
METHODS : This randomized , double - blinded study was conducted in 100 patients randomly allocated into five groups of 20 patients each . 