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: An anti - cephalothin IgG antibody was detected in the patient ' s serum and in the eluates from her erythrocytes .
### Output Text:
An anti - <span class="chemical">cephalothin</span> IgG antibody was detected in the patient ' s serum and in the eluates from her erythrocytes . 