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Lesson Review

Author:Jonathan Fong
ETP Title:How Much Caffeine Is in My Soft Drink?
Organization:University of California, Berkeley
ETP Type:Enhance Existing Curriculum
Grade Level(s):10,11,12
Subject Area(s):Science

Lesson Abstract:

"How Much Caffeine Is in My Soft Drink?" is a laboratory activity that utilizes chemical separation techniques and gas chromatography-mass spectrometry (GC/MS) to identify caffeine concentration in soft drinks. Chemistry concepts of density, molecular polarity, and solubility will be applied in the determination of caffeine content in soft drinks. Student samples will be sent to U.C. Berkeley for analysis. Relevant gas chromatogram data will be returned via e-mail, so students will use basic math, unit conversions, and dimensional analysis for the determination of caffeine. They will be interested in the real caffeine content in their soft drinks and hopefully excited when comparing their experimental content.

California Standards

Chemistry - Grades 9 Through 12 Science Content Standards Chemical Bonds 2. Biological, chemical, and physical properties of matter result from the ability of atoms to form bonds from electrostatic forces between electrons and protons and between atoms and molecules. As a basis for understanding this concept: e. Students know how to draw Lewis dot structures. f.* Students know how to predict the shape of simple molecules and their polarity from Lewis dot structures.

Measurable Objectives:

Objectives:

  • Students will use chemical separation techniques to detect caffeine in soft drinks.
  • Students will apply knowledge of solubility, molecular polarity, and density to explain separation techniques.
  • Students will determine caffeine content in soft drinks by analyzing gas chromatography/ mass spectrometry data.

Assessment:

Lab report about the experiment - grading subject to teacher's normal lab report guidelines. You can tailor the lab report to your way of having your students write their lab reports. I have Calculations and Lab Analysis questions that your students can incorporate into their lab reports.

Sample answers to Calculations and Lab Analysis are provided for teacher use only. (See document named "Caffeine Lab Answers.pdf".) I normally grade these parts of the lab report based on correctness of work shown, but you may wish to grade based on your preference.

The connection between the ETP and Fellowship. :

The Mass Spectrometry Facility at U.C. Berkeley has the capabilities of analyzing mutiple samples in succession on a GC/MS machine on the university campus. My fellowship at the Mass Spectrometry Facility at U.C. Berkeley has given me the project of writing a lesson for high school level chemistry curriculum involving GC/MS.  "How Much Caffeine Is in My Soft Drink?" will serve to connect chemical separation techniques taught in the California high school chemistry curriculum to GC/MS, which will be used to quantitatively measure experimental yield versus book value of caffeine content in a particular soft drink.

Instructional Plan:

Teacher Preparation of Materials (Approximate prep time: 15 minutes)

Do Step 1 one month in advance. The rest can be done 1 or 2 days prior to the lab.

  1. ***E-mail Dr. Ulla Andersen (norklit@berkeley.edu) at U.C. Berkeley Mass Spectrometry Facility to arrange shipment of GC-MS Autosampler 1.5-mL microvials (1 per lab group) and deuterated caffeine. Please contact 1 month prior to the lab just to be safe.
  2. Make sure you have apparatus materials (see previous page for list) needed for the experiment and the following reagents in your stockroom: anhydrous sodium carbonate (~1.5 g per class) and sodium sulfate (~1.0 g per class).
  3. Obtain 70% isopropyl alcohol or 2-propanol (commonly known as rubbing alcohol), easily found at drug stores, supermarkets. Each class will need ~20 mL.
  4. Have students sign up and bring soft drinks for analysis.

Background and Experiment (1 class period or about 45-50 minutes)

  1. Explain to your students:
  • the relevance of this experiment in determining the caffeine content in soft drinks they are likely to consume
  • density (Isopropanol is less dense than water, so isopropanol floats on water.) Optional Demonstration: If you want to illustrate this, you may want to demo or have each lab group put about 10 mL of soft drink in a test tube with 5 mL of rubbing alcohol. Cap and invert the test tube twice (just as students will do during the experiment), venting as needed to relieve pressure. Have students observe what happens.
  • solubility (Caffeine is more soluble in isopropanol than water. Sodium carbonate makes sugars and other compounds more soluble in water by making the pH more basic and attracting the water molecules more tightly to itself.)
  • molecular polarity (Caffeine is slightly polar, allowing it to dissolve more readily in isopropanol than water when the ionic compound sodium carbonate is added. Sodium carbonate is attracted to the water more, so the caffeine goes along with the isopropanol.)
  • what deuterated caffeine is (Normal caffeine has a molecular weight of 194 and deuterated caffeine has a molecular weight of 197. Deuterated caffeine has 3 deuterium atoms. Deuterium is a hydrogen atom with an extra neutron. The mass difference in deuterated caffeine allows us to use a similar molecule with similar structure for comparison.)
  • Explain GC-MS. Optional: Use attached Powerpoint titled "Caffeine GC-MS.ppt". It contains background information about GC-MS and goes over the procedures for the experiment.
  1. Students carry out the experiment in their student lab groups or pairs. Teacher pipets 100 µL of 1 mg/mL deuterated caffeine to each group, since this is substance is in limited quantity. The total procedure should take about 25 minutes.
  • Make sure each group labels their sealed GC-MS Autosampler 1.5-mL microvial with class period and sample number. Number samples consecutively starting from #1.
  1. Pack your caffeine samples in the same manner as you received the empty microvials. Mail (any except USPS) or self-deliver to U.C. Berkeley Mass Spectrometry Facility, c/o Dr. Ulla Andersen, B207 Stanley Hall, Berkeley, CA 94720. You will need to pay for the postage or deliver it yourself for free.

Analysis (½ class period about 1 week later)

  1. Within a week, you should receive an e-mail with your students' results. They can determine the experimental caffeine concentration in their soft drink by looking at the gas chromatograph and mass spectrum. They compare the ratio in sizes of the abundance peaks of normal caffeine (MW 194) with that of the abundance peak for the known concentration of deuterated caffeine (MW 197).
  2. Compare your students' experimental values to the book values for caffeine content in soft drinks (see PDF handout titled caffeine_content_drinks.pdf).
  3. Sample answers to the Calculations and Analysis questions for teacher reference are in the document titled "Caffeine Lab Answers.pdf".

Supplies:

• 100 µL automatic pipet with disposable tips (1 for instructor only)

Reagents (assuming 8 groups in the class) • Soft drinks (exactly 1.000 mL or 1/3 fl. oz.) – each group selects one to bring in • 70% isopropyl alcohol or 2-propanol, a.k.a. rubbing alcohol easily found at drug stores, supermarkets, etc. (~20 mL per class) • Anhydrous sodium carbonate (~1.5 g per class) • Sodium sulfate (~1.0 g per class) • deuterated caffeine, d3-caffeine (1 mg/mL concentration, 1 mL volume)*** ***Obtained for FREE from U.C. Berkeley Mass Spectrometry Facility E-mail Dr. Ulla Andersen (norklit@berkeley.edu) for information/to arrange. Contact her 1 month prior just to be safe.

Bibliographic or other resources you used in creating this curriculum:

Hill, Devon W., McSharry, Brian T., and Trzupek, Larry S. "Quantitative Analysis by Isotopic Dilution Using Mass Spectroscopy: The Determination of Caffeine by GC-MS." Journal of Chemical Education 65.10 (1988): 907-910. Print.

Horning, Marjorie G., Boucher, E. Ann, Stafford, Michele, and Horning, Evan C.. "A rapid procedure for the isolation of drugs and drug metabolites from plasma." Clinica Chimica Act, 37.3 (1972): 381-386. Web.

Laswick, Patty Hall and Laswick, John A. "Caffeine and benzoic acid in soft drinks." Journal of Chemical Education 49.10 (1972): 708. Print.

Yang, Min J., Orton, Maureen L., and Pawliszyn, Janusz. "Quantitative Determination of Caffeine in Beverages Using a Combined SPME-GC/MS Method." Journal of Chemical Education 74.9 (1997): 1130. Print.

"Caffeine Content of Drinks - How Much Caffeine in Coffee, Soft Drinks, Tea - Amount of Caffeine." wilstar.com. Wilstar. n.d. Web. 13 June 2011.

""Caffeine Lab Pre/Post-Lab Activities." departments.oxy.edu/tops/. Occidental College. 10 Apr. 2006. Web. 14 June 2011.

"Caffeine from Soda Preparation." studyblue.com. Study Blue. n.d. Web. 14 June 2011.

"Caffeine in the diet: MedlinePlus Medical Encyclopedia." nlm.nih.gov. Medline Plus. 23 June 2011. Web. 23 June 2011.

"Caffeine overdose: MedlinePlus Medical Encyclopedia." nlm.nih.gov. Medline Plus. 23 June 2011. Web. 23 June 2011.

"Caffeine Content of Drinks." energyfiend.com. Energy Fiend, n.d. Web. 20 June 2011.

The needs this ETP will fulfill in the classroom, teaching or school:

"How Much Caffeine Is in My Soft Drink?" utilizes university and industry-standard machines and techniques to solve a relevant question that a high school student might wonder about.  With that in mind, the connection between high school to everyday life for the student can be made.  The experimental results of the amount of caffeine students isolate in a particular soft drink would be of great interest for my students. It would also help them practice solid, meticulous laboratory techniques.  This lesson will use GC/MS machines at U.C. Berkeley to provide students data to calculate caffeine content in a particular beverage.

Keywords:

chemical separation, caffeine, soft drink, density, polarity, solubility, unit conversions

Attachments: