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: In vitro hydrolysis of ED was done in aqueous buffers ( pH 1 . 2 , 7 . 4 , 9 ) and in 80 % ( v / v ) human plasma ( pH 7 . 4 ) .
### Output Text:
In vitro hydrolysis of ED was done in aqueous buffers ( pH 1 . 2 , 7 . 4 , 9 ) and in 80 % ( v / v ) human plasma ( pH 7 . 4 ) . 