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: During her further 3 weeks inpatient admission the serum sodium ranged from 134 to 137 mmol / L during treatment with mirtazapine .
### Output Text:
During her further 3 weeks inpatient admission the serum <span class="chemical">sodium</span> ranged from 134 to 137 mmol / L during treatment with <span class="chemical">mirtazapine</span> . 