The peaks have been assigned as follows:

 <A href="http://wwwchem.uwimona.edu.jm:1104/spectra/chime2/butane.pdb"></A>
Reset display 15CH3,
27C2H3, 28C2H4,
29 C2H5, 43C3H7,
58 C4H10

n-butane RMM= 58.12
The MS of n-butane is given above.