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: Thus , FS containing 47 . 5 mg / ml tAMCA evoked generalized seizures in all tested rats ( n = 6 ) while the lowest concentration of tAMCA ( 0 . 5 mg / ml ) only evoked brief episodes of jerk - correlated convulsive potentials in 1 of 6 rats .
### Output Text:
Thus , FS containing 47 . 5 mg / ml <span class="chemical">tAMCA</span> evoked generalized seizures in all tested rats ( n = 6 ) while the lowest concentration of <span class="chemical">tAMCA</span> ( 0 . 5 mg / ml ) only evoked brief episodes of jerk - correlated convulsive potentials in 1 of 6 rats . 