[r-kaede]

i have this very simple ESI- MASS SPECTRUM , with M+ ion at m/z= 151, a very small peak at m/z=152(probably satellite isotope), base peak at =109 (at small peaks at 110 and 108), another peak at 80 (accompanied by small peaks at 81,82) and another peak at 43.

i need to identify this compound, but i'm really lost at how, i think there is probably an acetate (CH3CO) in the compound but i'm not sure...

if anyone can help me with step by step instruction on how you get the answer will be very much appreciated. thanks..

[MOTOBALL]

Back to basics first, for an ESI spectrum

(1) m/z 151 is [M + H]+ NOT M+; this means MW = 150 Da

(2) EVEN MW (150 Da) requires EVEN number of N atoms (N = 0, 2, 4, 6 etc)

(3) your comments about the isotope peaks (152, 110, 81) are correct

(4) m/z 151  :rarrow:m/z 109 (loss of 42 Da is CH2= C=O), correctly interpreted as due to presence of -O-C(O)CH3 (possibly also -NHC(O)CH3)

(5) m/z 80 is (151 - 71) or (109 - 29); loss of 29 Da is difficult to explain under ESI

are you sure this is ESI and not Electron ionization (EI) ??

(6) m/z 43 is likely CH3CO+; confirms (4) above

Difficult to proceed from here w/o more info; do you have an actual spectrum; if so,

(a) measure the intensity ratio of 151 to 152 and divide that ratio by 1.1 to get approximate C atom count

(b) if m/z 153 is smaller than m/z 152, then probably S is absent

(c) construct a table of C, H, N, O values that will give MW 150

[r-kaede]

sorry , just checked back with question, it is ei mass spectrum... sorry..

i know already what the molecule is, it is acetaminophen.. i randomly search for it at a molecule database, and i actually found the mass spec for it...but still couldnt explaine the m/z= 80 for the molecule i'll attach a link for it

http://webbook.nist.gov/cgi/cbook.cgi?Spec=C103902&Index=0&Type=Mass&Large=on

thanks for the help...