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: This study analyzed the incidence of neurological complications during ALL treatment in a single pediatric institution , focusing on clinical , radiological , and electrophysiological findings .
### Output Text:
This study analyzed the incidence of neurological complications during ALL treatment in a single pediatric institution , focusing on clinical , radiological , and electrophysiological findings . 