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: Here , we aimed to re - investigate the diagnostic value of verapamil in a population who were all screened for macroprolactinemia .
### Output Text:
Here , we aimed to re - investigate the diagnostic value of <span class="chemical">verapamil</span> in a population who were all screened for macroprolactinemia . 