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 study was undertaken as part of neonatal screening for hearing impairment and involved both ears of 200 newborns .
### Output Text:
METHODS : This study was undertaken as part of neonatal screening for hearing impairment and involved both ears of 200 newborns . 