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

Results and Discussion
These compounds tend to lose hydrogen producing m/z 217, m/z 281 and m/z 371
respectively as shown in figure 3-12. A molecular ion was as well formed in
addition to the dominant [M-H] + ion for each of the three hydrocarbons. 5-α-
Cholestane was previously measured by the group of kenttamaa where no ions
were detected under positive APCI conditions according to their experimental
results. 96
Intens.
[%]
100
10
329.3
+MS
80
60
40
20
0
6
7
203.2
273.3
189.2
279.3
323.4
295.3
225.3 242.9 257.2
315.3
183.2
9
4 5
2 3
180 200 220 240 260 280 300 320 340 360 m/z
335.4
345.3
365.4
Figure 3-11 APCI spectrum of the eight Chiron hydrocarbon mixture (for
structures see figure 3-10)
Overall it was observed that the relative product ion abundances of the analytes
(equimolar solution at 0.2 mM) were very close to each other. Further direct
infusion experiments were performed using a mixture of high MW n-alkanes (C50-
C60 mass range) that were dissolved in n-heptane. Examination of separate and
model mixture of these n-alkanes demonstrated that the same ionisation pattern
was shown. The APCI mass spectrum comprised [M-H] + ions that are shown in
figure 3-13. Each gas phase [M-H] + ion was, similar to the previous hydrocarbons
in the other groups, accompanied by its molecular ion M •+ . For example
pentacontane produced a stable m/z 701.8 as intact ion conforming to [C 50 H 101 ] +
ion, this ion was accompanied by a lower-intensity M •+ m/z 702.8 conforming to
[C 50 H 102 ] •+ . This pattern of ionisation produced for all of the examined high mass
n-alkanes wasn’t surprising as this is consistent with our previous investigation of
n-alkanes’ behaviour under APCI-TOF-MS.
46