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: Immunohistochemical staining indicated loss of GFAP - staining already at 30 min after induction of seizures in an oval focus situated in the center of SNR while sparing medial and lateral aspects .
### Output Text:
Immunohistochemical staining indicated loss of GFAP - staining already at 30 min after induction of seizures in an oval focus situated in the center of SNR while sparing medial and lateral aspects . 