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: Cefotetan - dependent antibodies were detected in the patient ' s serum and in an eluate prepared from his red blood cells .
### Output Text:
<span class="chemical">Cefotetan</span> - dependent antibodies were detected in the patient ' s serum and in an eluate prepared from his red blood cells . 