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: INTERVENTIONS : Pupil diameter was monitored using a computerized infrared pupillometer over 4 hours .
### Output Text:
INTERVENTIONS : Pupil diameter was monitored using a computerized infrared pupillometer over 4 hours . 