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: dP / dtejc outcome was combined with the ECG results , giving an ECG - enhanced value , and compared to ECG alone .
### Output Text:
dP / dtejc outcome was combined with the ECG results , giving an ECG - enhanced value , and compared to ECG alone . 