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: Clinical assessment as well as blinded ratings of Unified Parkinson ' s Disease Rating Scale ( UPDRS ) scores were carried out pre - and postoperatively .
### Output Text:
Clinical assessment as well as blinded ratings of Unified Parkinson ' s Disease Rating Scale ( UPDRS ) scores were carried out pre - and postoperatively . 