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: Intradermal glutamate and capsaicin injections : intra - and interindividual variability of provoked hyperalgesia and allodynia .
### Output Text:
Intradermal <span class="chemical">glutamate</span> and <span class="chemical">capsaicin</span> injections : intra - and interindividual variability of provoked hyperalgesia and allodynia . 