What’s in my vanilla? Practice exercise.
1. Complete table 1.
Table 1# of protons / #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?
- 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 (%)
*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) / Species / Measurement (mm)
79 / 79Br+
*Experimental molar mass of Br:
Accepted molar mass of Br:
*Percent error in molar mass
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?