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: For capsaicin , secondary pinprick hyperalgesia was detected with all von Frey gauges ( P < 0 . 001 ) .
### Output Text:
For <span class="chemical">capsaicin</span> , secondary pinprick hyperalgesia was detected with all von Frey gauges ( P < 0 . 001 ) . 