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: HBsAg , anti - HBs , anti - HBc , and anti - HIV 1 / 2 were determined as part of routine diagnosis using Axsym assays ( Abbott Laboratories , North Chicago , IL ) .
### Output Text:
<span class="chemical">HBsAg</span> , anti - HBs , anti - HBc , and anti - HIV 1 / 2 were determined as part of routine diagnosis using Axsym assays ( Abbott Laboratories , North Chicago , IL ) . 