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: The availability of newer rapid diagnostic techniques , such as polymerase chain reaction , may make earlier , more effective treatment of adenovirus infection possible .
### Output Text:
The availability of newer rapid diagnostic techniques , such as polymerase chain reaction , may make earlier , more effective treatment of adenovirus infection possible . 