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: The diagnosis of droperidol - induced psychological disturbance was not made straight away although on subsequent close questioning the patient gave a very clear history .
### Output Text:
The diagnosis of <span class="chemical">droperidol</span> - induced psychological disturbance was not made straight away although on subsequent close questioning the patient gave a very clear history . 