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: Corresponding non - lithium pretreated groups were generated .
### Output Text:
Corresponding non - <span class="chemical">lithium</span> pretreated groups were generated . 