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: Steady state arterial plasma concentrations of atrial natriuretic factor were 39 + / - 10 pg / ml ( n = 6 ) during infusions of saline and 284 + / - 24 pg / ml ( n = 6 ) and 1520 + / - 300 pg / ml ( n = 9 ) during 0 . 03 and 0 . 1 microgram / kg / min infusions of the factor . ( ABSTRACT TRUNCATED AT 250 WORDS )
### Output Text:
Steady state arterial plasma concentrations of atrial natriuretic factor were 39 + / - 10 pg / ml ( n = 6 ) during infusions of saline and 284 + / - 24 pg / ml ( n = 6 ) and 1520 + / - 300 pg / ml ( n = 9 ) during 0 . 03 and 0 . 1 microgram / kg / min infusions of the factor . ( ABSTRACT TRUNCATED AT 250 WORDS ) 