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: Effect of doxorubicin on [ omega - I - 131 ] heptadecanoic acid myocardial scintigraphy and echocardiography in dogs .
### Output Text:
Effect of <span class="chemical">doxorubicin</span> on <span class="chemical">[ omega - I - 131 ] heptadecanoic acid</span> myocardial scintigraphy and echocardiography in dogs . 