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: A total of 38 consecutive patients who presented to our clinic with impotence received 0 . 2 ml . of a combination of 3 drugs : 6 mg . papaverine , 100 micrograms . phentolamine and 10 micrograms . prostaglandin E1 with ( pH 7 . 05 ) or without ( pH 4 . 17 ) the addition of sodium bicarbonate ( 0 . 03 mEq . ) .
### Output Text:
A total of 38 consecutive patients who presented to our clinic with impotence received 0 . 2 ml . of a combination of 3 drugs : 6 mg . <span class="chemical">papaverine</span> , 100 micrograms . <span class="chemical">phentolamine</span> and 10 micrograms . <span class="chemical">prostaglandin E1</span> with ( pH 7 . 05 ) or without ( pH 4 . 17 ) the addition of <span class="chemical">sodium bicarbonate</span> ( 0 . 03 mEq . ) . 