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: CONCLUSIONS : It was determined that injection duration had an effect on bruising and pain following the subcutaneous administration of heparin .
### Output Text:
CONCLUSIONS : It was determined that injection duration had an effect on bruising and pain following the subcutaneous administration of <span class="chemical">heparin</span> . 