Gschwend%20thesis.pdf

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and l49 (M+41) ions in the CH4 chemical ionization (CI) spectrum and m/e
108 in the electron impact (El) spectrum (figure 2-8). Loss of l3
and 27 mass units (giving m/e 95 and 81) in the CI spectrum indicates
the presence of a terminal ethenyl group (Field, 1968), while loss of
15 mass units (giving m/e 93) in both the EI and CI spectra suggests
that there is a terminal methyl substituent also. Due to insufficient
sample size, the remainder of the EI spectrum was largely uninter-
pretable. Authentic trans ,cis-I, 3 ,5-octatriene and ethyl benzene
CI spectra are also shown in figure 2-8. These spectra have all the
same major fragment peaks as the unknown and èthyl benzene mixture in
the sample. However, since this octatriene does not coelute with
ethyl benzene, the unknown cannot be this particular isomer. Al though
not all cyclic and branched structures can be ruled out, these data
are consistent with a structure such as a straight chain octatriene.
The GC peak heights of this unknown compound (ro 108) were estimated
by subtracting assumed ethyl benzene peak heights from that of the
mixed GC peak. The ethyl benzene peak heights were obtained by assuming
that they were proportional to the peak heights of the other C2-benzene
isomers. This was reasonable because ethyl benzene levels covary with
the other C2-benzene isomer concentrations in most fossil fuels and
environmental samples tested (chapter 4). These difference estimates
agree well with predicted peak heights based on GCMS where data were
available. The resultant spatial distribution of the concentration
of this unknown compound (ro 108) is shown in figure 2-7. Maximum
values were always found near the surface. Station 3 showed the
highest level of all surface samples ând the concentrations decreased
in the offshore direction.