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: There were no significant differences in renal sodium excretion , oxygen consumption , or urinary flow rates in kidneys perfused with suprofen compared with the drug - free control groups .
### Output Text:
There were no significant differences in renal <span class="chemical">sodium</span> excretion , <span class="chemical">oxygen</span> consumption , or urinary flow rates in kidneys perfused with <span class="chemical">suprofen</span> compared with the drug - free control groups . 