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: Reproducibility across and within volunteers ( inter - and intra - individual variation , respectively ) was assessed using intraclass correlation coefficient ( ICC ) and coefficient of variation ( CV ) .
### Output Text:
Reproducibility across and within volunteers ( inter - and intra - individual variation , respectively ) was assessed using intraclass correlation coefficient ( ICC ) and coefficient of variation ( CV ) . 