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: Both groups receiving 10 micrograms kg - 1 showed increases in heart rate of up to 30 beat min - 1 ( 95 % confidence limits 28 - 32 beat min - 1 ) .
### Output Text:
Both groups receiving 10 micrograms kg - 1 showed increases in heart rate of up to 30 beat min - 1 ( 95 % confidence limits 28 - 32 beat min - 1 ) . 