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: Prolactin results were compared with those of a previous personal cohort of 1 , 340 patients with erectile dysfunction and systematic prolactin determination .
### Output Text:
Prolactin results were compared with those of a previous personal cohort of 1 , 340 patients with erectile dysfunction and systematic prolactin determination . 