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: We determined the BChE activity and the BCHE genotype using molecular genetic methods , the duration of apnea , time to sufficient spontaneous ventilation and whether neuromuscular monitoring was used .
### Output Text:
We determined the BChE activity and the BCHE genotype using molecular genetic methods , the duration of apnea , time to sufficient spontaneous ventilation and whether neuromuscular monitoring was used . 