What’s in my vanilla? Practice exercise.
1. Complete table 1.
Table 1
# of protons
20
Ne
21
Ne
22
Ne
#of neutrons
Exact mass
% abundance
2. Figure 1 shows the mass spectrum of neon. Which isotope is present in the most
abundance? In the least abundance?
Figure 1. Mass Spectrum of Neon
3. The mass spectrum of mercury is shown in figure 2. Use a ruler to help you
complete table 2. Be sure to use correct sig figs. when doing addition, division,
etc.
Figure 2. Mass Spectrum of Mercury.
Table 2.
Isotope
Mass (amu)
Measurement (mm)
Isotopic Abundance (%)
198Hg+
*Experimental molar mass of mercury:
Accepted molar mass of mercury:
*Percent error in molar mass:
Most abundant isotope of mercury:
Isotope closest to the molar mass:
*Sample calculation (include one example of % isotopic abundance; MM Hg ; % error)
4. The mass spectrum of elemental bromine (Br2) is shown in figure 3. Use a ruler to
help you complete table 3. Be sure to use correct sig figs.
Figure 3. Mass spectrum of Br2
Table 3.
Mass (amu)
79
Species
79Br+
*Experimental molar mass of Br:
Accepted molar mass of Br:
*Percent error in molar mass
*Sample calculations:
Measurement (mm)
5. A. What is the molecular mass of vanillin containing all carbon-12? What is the
molecular mass of vanillin containing one carbon-13?
B. Describe what you would expect the peaks in the mass spectrum of vanillin to look
like.
C. Would you expect to see a peak in the mass spectrum for vanillin containing two
carbon-13 atoms? Why or why not?
6. Your lab group should have received packets of GC/MS data containing
chromatograms and accompanying mass spectra for five different samples:
1) Real vanilla extract
2) Imitation vanilla extract
3) Vanilla bean
4) Real vanilla extract contaminated with Coumarin.
Use these data packets to answer the following questions.
A. What is the difference between a chromatogram and a mass spectrum?
B. Why is there only one chromatogram but multiple mass spectra in each packet?
C. What does each peak in the chromatogram represent? What does each peak in the
mass spectrum represent?
D. The main flavor component in vanilla is vanillin, C3H8O3. What is the retention time
for the vanillin? How did you identify it?
E. If the molecular mass of vanillin is 152 amu, why is there a large 151 peak in the mass
spectrum of vanillin? What is the 153 peak?
F. Is the vanillin present in all of the samples? What does this mean about the main
flavor component in imitation compared to real vanilla?
G. If the molecular formula of coumarin is C9H6O2, how can you identify the coumarin
contaminant in the real vanilla extract?
H. Are there any differences between the real vanilla extract, the imitation vanilla
extract, and the vanilla bean? What are they and what do you think they represent?
Would these differences be reflected in any flavor differences?