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: Captopril ( 50 mg / kg / day , given orally ) , an inhibitor of angiotensin - converting enzyme used as a standard cardioprotective drug , was used as a positive control in this study .
### Output Text:
<span class="chemical">Captopril</span> ( 50 mg / kg / day , given orally ) , an inhibitor of <span class="chemical">angiotensin</span> - converting enzyme used as a standard cardioprotective drug , was used as a positive control in this study . 