Development of a Novel Mass Spectrometric ... - Jacobs University

Results and Discussion
Within all of the three mass spectra (Figures 3-11, 3-12 and 3-13), the major
product ion of each analyte was found characteristic for the original precursor
hydrocarbon within the three model mixtures. All yielded a unique [M-H] +
ionisation pattern. Also figure 3-14 demonstrates the production of the same
product ion when the three groups were added together.
Again the ideal behaviour of these analytes is mostly attributed to the optimised
APCI developed methodology. A minor change of any of the method parameters
can hugely affect the product ion generation process. The examined seventeen
compounds presented model compounds of linear, branched and cyclic
hydrocarbons. Table 3.2 presents all the hydrocarbons examined in this experiment
showing their unique product ion distribution. Some of these hydrocarbons are
representative or similar to components in real life complex mixtures such as
petroleum mixtures. Since n-alkanes in the previous section and the other
hydrocarbons in the current section have been ionised by a unique [M-H] +
ionisation, an insight about the mechanism for the formation of this major ion and
other ions will be discussed in the next section.
Table 3.2 Ions produced of model hydrocarbon compounds
# Analyte MW Product Ion
1 2,6,10,14-Tetramethyl hexadecane 282 M-H +
2 2,6,10,14-Tetramethyl nonadecane 324 M-H +
3 2,6,10,14,18-Pentamethyl heneicosane 366 M-H +
4 n-Tetradecyl cyclohexane 280 M-H +
5 n-Octadecyl cyclohexane 336 M-H +
6 n-Octyl benzene 190 M-H +
7 n-Nonyl benzene 204 M-H +
8 n-Decyl benzene 218 M-H +
9 n-Tetradecyl benzene 274 M-H +
10 n-Octadecyl benzene 330 M-H +
11 5-α-Cholestane 372 M-H +
12 Dotetracontane 590 M-H +
13 Tetratetracontane 618 M-H +
14 Octatetracontane 674 M-H +
15 Pentacontane 702 M-H +
16 Tetrapentacontane 758 M-H +
17 Hexacontane 842 M-H +
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