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: Cerebrospinal fluid was obtained for pharmacokinetic analysis , and pain ratings in response to acute heat stimuli and areas of mechanical hyperalgesia and allodynia after intradermal capsaicin injection were determined .
### Output Text:
Cerebrospinal fluid was obtained for pharmacokinetic analysis , and pain ratings in response to acute heat stimuli and areas of mechanical hyperalgesia and allodynia after intradermal <span class="chemical">capsaicin</span> injection were determined . 