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: Identification of a simple and sensitive microplate method for the detection of oversulfated chondroitin sulfate in heparin products .
### Output Text:
Identification of a simple and sensitive microplate method for the detection of oversulfated <span class="chemical">chondroitin sulfate</span> in <span class="chemical">heparin</span> products . 