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 coma was prevented with 1 . 68 mmol L - dopa given by gastric intubation 15 minutes before the ammonium salt injection .
### Output Text:
This coma was prevented with 1 . 68 mmol <span class="chemical">L - dopa</span> given by gastric intubation 15 minutes before the <span class="chemical">ammonium salt</span> injection . 