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: In 10 of 11 patients , BAEP waves II / III - V completely disappeared within 2 to 25 min after papaverine .
### Output Text:
In 10 of 11 patients , BAEP waves II / III - V completely disappeared within 2 to 25 min after <span class="chemical">papaverine</span> . 