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: In linear regression analyses the CGI - SF score was not affected significantly by the duration of SD , type of SSRI used and age .
### Output Text:
In linear regression analyses the CGI - SF score was not affected significantly by the duration of SD , type of <span class="chemical">SSRI</span> used and age . 