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: In contrast , a simultaneous multivariable analysis identified IF , MIC , and total dose according to one model and ln ( mean Cmax / MIC ) according to a second statistical model of parameters selected to have the greatest prospective value .
### Output Text:
In contrast , a simultaneous multivariable analysis identified IF , MIC , and total dose according to one model and ln ( mean Cmax / MIC ) according to a second statistical model of parameters selected to have the greatest prospective value . 