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: The occurrence of nephrotoxicity was similar between the conventional and extended - interval groups , at 10 % and 5 % , respectively ( P = 1 . 00 ) .
### Output Text:
The occurrence of nephrotoxicity was similar between the conventional and extended - interval groups , at 10 % and 5 % , respectively ( P = 1 . 00 ) . 