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: RESULTS : Two hundred twenty - eight patients ( 42 % men ) with a mean age of 81 . 1 ( range 76 - 94 ) were included in the analysis .
### Output Text:
RESULTS : Two hundred twenty - eight patients ( 42 % men ) with a mean age of 81 . 1 ( range 76 - 94 ) were included in the analysis . 