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: The relationship of arthritis and sexual dysfunction was investigated among 169 patients with rheumatoid arthritis , osteoarthritis and spondyloarthropathy , 130 of whom were pair - matched to controls .
### Output Text:
The relationship of arthritis and sexual dysfunction was investigated among 169 patients with rheumatoid arthritis , osteoarthritis and spondyloarthropathy , 130 of whom were pair - matched to controls . 