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: Subjects were able to reliably discriminate pain magnitude and duration across capsaicin doses ( both p < 0 . 001 ) , regardless of whether first - time ratings were requested immediately , after one hour or after one day .
### Output Text:
Subjects were able to reliably discriminate pain magnitude and duration across <span class="chemical">capsaicin</span> doses ( both p < 0 . 001 ) , regardless of whether first - time ratings were requested immediately , after one hour or after one day . 