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: He then presented to the emergency department feeling quite ill and was found to have a blood urea nitrogen ( BUN ) concentration of of 147 mg / dl , creatinine of 15 . 3 mg / dl and serum potassium of 8 . 7 mEq / l .
### Output Text:
He then presented to the emergency department feeling quite ill and was found to have a <span class="chemical">blood urea nitrogen</span> ( <span class="chemical">BUN</span> ) concentration of of 147 mg / dl , <span class="chemical">creatinine</span> of 15 . 3 mg / dl and serum <span class="chemical">potassium</span> of 8 . 7 mEq / l . 