Characterization of Complex Organic Mixtures

Overview

This activity was prepared by David Walker (LASA High School) and Rose Cory (University of Michigan), based on work conducted at Toolik Field Station in Alaska. The purpose is to introduce students to Van Krevelen diagrams, which are used to interpret results of high resolution mass spectrometry and characterize the compound classes present in complex organic mixtures. Students will create Van Krevelen diagrams depicting different classes of compounds and learn to recognize patterns in these diagrams. They will then use their knowledge to characterize the organic composition of a sample of stream water.

Background Resources for the Instructor

1. Mass Spectrometry Introduction (Michigan State University)
2. Mass Spectrometry Overview (Royal Society of Chemistry)
3. Finding the Molecular Formula from a Mass Spectrum (University of St. Thomas)
4. Characterization of Complex Organic Mixtures via Mass Spectrometry
5. Photodegradation of Permafrost DOC Yield Bacterial Fuel
   
   

Objectives

Students will able able to:

1. Prepare a Van Krevelen diagram for a series of compounds.

2. Draw conclusions regarding the general location of aromatic vs. aliphatic compounds on a Van Krevelen diagram.

3. Draw conclusions regarding compound oxidation and location on a Van Krevelen diagram.

4. Define general compound classes present in complex organic mixtures found in nature.

5. Diagram general compound class regions on a Van Krevelen diagram.

6. Distinguish between compound classes based on their aromaticity and oxidation.

7. Draw conclusions regarding the aromatic vs. aliphatic organic content in a water sample.

8. Draw conclusions regarding the organic compound classes present in the water sample.
   
   

Lesson Preparation

Before beginning this activity, students should have a fundamental understanding of mass spectrometry and how this technology can be used to determine the molecular formula of a simple organic unknown. Students should also be able to identify a compound as aromatic or aliphatic, based on its structure.

Procedure

1. Students should work in pairs to complete the activity. Provide each student with an activity packet (see lesson attachments). Provide each student pair with a calculator and a computer with internet access.

2. Give students at least 40 minutes to complete Activity 1. Subsequently, review the activity with the entire class using the answer key (see lesson attachments).

3. Give students at least 60 minutes to complete Activity 2. Subsequently, review the activity with the entire class using the answer key (see lesson attachments).

4. Give students at least 20 minutes to complete Activity 3. Subsequently, review the activity with the entire class using the answer key (see lesson attachments).
   
   

Assessment

Collect students activity packets and grade for completion and accuracy.

Extension

This lesson could be easily extended to address current research on climate change and the permafrost positive feedback loop in the Arctic. Student groups could use their knowledge of Van Krevelen diagrams to evaluate the Van Krevelen data present in Ward, et al., 2017 (see lesson resources).

Transferability

As written, this activity works best in a classroom environment. For informal educators, this activity could easily work in concert with a field trip to a local college or university laboratory.

Resources

Mass Spectrometry. Michigan State University. https://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/Spectrpy/MassSpec/masspec1.htm

Minor, Elizabeth C., et al. “Structural Characterization of Dissolved Organic Matter: a Review of Current Techniques for Isolation and Analysis.” Environ. Sci.: Processes Impacts, vol. 16, no. 9, 2014, pp. 2064–2079.

Ward, Collin P., and Rose M. Cory. “Chemical Composition of Dissolved Organic Matter Draining Permafrost Soils.” Geochimica Et Cosmochimica Acta, vol. 167, 2015, pp. 63–79.

Ward, Collin P., et al. “Photochemical Alteration of Organic Carbon Draining Permafrost Soils Shifts Microbial Metabolic Pathways and Stimulates Respiration.” Nature Communications, vol. 8, no. 1, 2017.

Sparkman, O. David. Mass Spectrometry Desk Reference. Global View Publ., 2007.

Credits

This activity was created by David Walker (LASA High School) and Rose Cory (University of Michigan), based on work conducted during Summer 2019 at Toolik Field Station in Alaska.

David Walker
Science Teacher
LASA High School
7309 Lazy Creek Drive #225
Austin, TX 78724
david.walker [at] austinisd.org

Rose Cory
Associate Professor
University of Michigan
2534 C.C. Little Building 1100 North University Avenue
Ann Arbor, MI 48109
rmcory [at] umich.edu