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: SRL - treated rats presented proteinuria and NGAL ( serum and urinary ) as the best markers of renal impairment .
### Output Text:
<span class="chemical">SRL</span> - treated rats presented proteinuria and NGAL ( serum and urinary ) as the best markers of renal impairment . 