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: Peripheral neuropathy due to nutritional deficiency of thiamine and riboflavin was common ( 10 . 1 % ) and presented mainly as sensory and sensori - motor neuropathy .
### Output Text:
Peripheral neuropathy due to nutritional deficiency of <span class="chemical">thiamine</span> and <span class="chemical">riboflavin</span> was common ( 10 . 1 % ) and presented mainly as sensory and sensori - motor neuropathy . 