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: This study was done to assess the influence of a high intracoronary cocaine concentration on LV systolic and diastolic function in humans .
### Output Text:
This study was done to assess the influence of a high intracoronary <span class="chemical">cocaine</span> concentration on LV systolic and diastolic function in humans . 