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: PATIENTS : Neurocritical care patients admitted between July 2009 and September 2012 were evaluated and then matched 1 : 1 based on propensity scoring of baseline characteristics .
### Output Text:
PATIENTS : Neurocritical care patients admitted between July 2009 and September 2012 were evaluated and then matched 1 : 1 based on propensity scoring of baseline characteristics . 