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 serum FBAL concentration subsequently decreased to 352 ng / ml , the same as the value measured on the first day of S - 1 administration .
### Output Text:
The serum <span class="chemical">FBAL</span> concentration subsequently decreased to 352 ng / ml , the same as the value measured on the first day of S - 1 administration . 