3.2: Week 1 - Money

Lab Manual: Analytical Chemistry at Duke · LibreTexts

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    From LibreTexts, under CC BY-NC-SA, as the source states it; its equations are written in TeX, which the PDF shows typeset. This page at LibreTexts.

    Pre-lab Assignment:

    📅 Due: This pre-lab assignment is due prior to the Week 1 Dry Lab meeting.

    🎯 Purpose: The first two questions in this pre-lab assignment are designed to engage you in thinking about how organic compounds, such as cocaine, interact with paper currency at the molecular level. By analyzing the chemical structures of both the contaminant and the currency material, you will apply your understanding of intermolecular forces to explain why some organic substances adhere strongly and persistently to surfaces like paper. These foundational chemical principles will help you understand the behavior of trace organic compounds in real-world forensic and analytical contexts.

    Questions:
    1. What molecular-level interactions contribute to the adsorption of cocaine onto paper currency? In your response, include the chemical structures of cocaine and cellulose (the primary component of paper). Draw a representation of how cocaine may interact with the cellulose surface. Identify and explain the intermolecular forces (e.g., hydrogen bonding, van der Waals interactions, ionic interactions) that are likely responsible for the adsorption and retention of cocaine on the surface of currency.
    2. Make a prediction about what organic compounds you will find on your currency during this experiment, using evidence to support your prediction. Use Web of Science or another literature database to research substances that contaminate currency, and might be found on your money.

    🎯 Purpose: The second group of questions in this pre-lab assignment will help you practice using scientific literature to justify key decisions in analytical method design. By exploring how researchers select instruments, prepare samples, and use internal standards, you will learn how to propose a method that balances accuracy, safety, cost, and practicality. These skills will support your ability to justify experimental choices in your scientific manuscript. 

    Questions:

    Use a research database to access the articles cited below and add them to your Zotero Library. Use these papers as reference for selection of your analytical methods and sample preparation protocols. You do not need to read these papers from start to finish. Read the sections of the papers that help you with this assignment.

    Papers:

    • Parker, Patrick D., Brandon Beers, and Matthew J. Vergne. “What Is in Your Wallet? Quantitation of Drugs of Abuse on Paper Currency with a Rapid LC–MS/MS Method.” Journal of Chemical Education 94, no. 10 (2017): 1522–26. https://doi.org/10.1021/acs.jchemed.7b00196
    • Negrusz, A, JL Perry, and CM Moore. “Detection of Cocaine on Various Denominations of United States Currency.” Journal of Forensic Sciences 1972-2005 43, no. 3 (1998): 626–29. https://doi.org/10.1520/JFS16193J.
    1. What instrument will you use?
      1. What kind of instrument detector enables specific identification and quantitation of trace organic analytes?
      2. What kind of instrument component can separate compounds in a mixture so that they can be analyzed by the detector described in (a).
      3. Propose an instrument that you will use to detect and quantify trace organic compounds on your currency. Justify why this instrument is the right choice for specific identification and quantitation of very low concentrations of organic analytes.

    2. Suggest a procedure to prepare the sample; the protocol (1) will extract organic material from currency, (2) is simple and low cost, (3) avoids the use of particularly hazardous solvents (like dichloromethane or chloroform), (4) takes less than 30 minutes to prepare a sample, and (5) does not destroy the currency.

    3. In the two manuscripts above, what internal standards were used during calibration and quantitation? 

    4. Will you use an internal standard? Decide whether you think an internal standard is necessary. Justify your answer with evidence from the papers or from other reliable sources.

    👥 Dry-Lab Group Discussion:

    In this discussion, you will collaborate with your research team to refine your understanding of how organic compounds interact with paper currency and you will refine your extraction protocol and analysis method. By drawing molecular interactions, evaluating extraction protocols, and discussing calibration strategies, you will apply chemical principles and literature evidence to make informed decisions about your experimental approach. This discussion should will be facilitated in small groups (2-4 students) by a member of the instructional team.

    Instructions:

    • Begin the session by grouping up and comparing the answers to your pre-lab questions in your group for ~5 minutes.
    • Assign roles (scribe, reporter, spokesperson, time keeper)
      • The Time Keeper will start a timer and encourage group consensus.
      • The Scribe will record the group work.
      • The Spokesperson will summarize your group’s discussion and questions to the instructors. 
      • The reporter will submit the group record at the end of class.
    • Write your work on the board and try to come to consensus as a group.
    • If you have trouble reaching consensus, consult another group for advice, or consult an instructor when they are available.

    Goals for Dry-Lab discussion:

    1. Team consensus about method choice: Which instrument is best for this application, considering availability of instruments in the undergraduate learning labs?
    2. Team consensus about extraction protocol: How will you prepare the sample?
    3. Team consensus on calibration strategy: Will you use an internal standard?
    Group Discussion Prompts
    1. Predict the relative amounts of cocaine and methamphetamine you will find on your currency. Using your pre-lab response as a starting point, draw on the board:
      1. A molecular-level picture of how cocaine is adsorbed onto cellulose-based currency. Include chemical structures and show the intermolecular interactions.
      2. Do a similar analysis for methamphetamine and cellulose. Do you expect methamphetamine to absorb onto cellulose as well as cocaine does? Justify your prediction using the molecular structures as the basis.
      3. Predict the relative amounts of methamphetamine and cocaine on paper currency.
    2. What instrument will you use, and what are the appropriate settings? Consider the instruments to which our course has access, and use the literature methods as a starting place.  How will you need to modify instrument settings to see them maximum number of possible contaminants?
    3. Discuss your proposed extraction protocol with your group, consider the limitations stated below, and finally consult your instructors. Discuss what are the costs and benefits of the suggested approaches and come to a group consensus about what protocol your team will use.
      1. Limitations of the analytical method: For example, if using gas chromatography, the sample should be dissolved in a solvent with a low boiling point so that the solvent elutes quickly and does not interfere with detection of the analyte ions. If using liquid chromatography, common mobile phases are water, methanol, and acetonitrile.
      2. Limitations of analytical solution preparation: If the solvent is too volatile, it will be challenging to transfer quantitatively, and difficult to prevent evaporation (which would affect concentration).
      3. Limitations imposed by purchased standards: Since we cannot purchase these controlled substances without a license, the standards are purchased as dilute solutions. The standard solutions (cocaine, methamphetamine) are only available as dissolved in Methanol - this solvent is versatile and suitable for both GC and LC applications.
      4. Solubility: The solutes must be soluble in the solvent.
      5. Safety: Some solvents are not only flammable, but also particularly toxic. Do not use solvents that are particularly toxic, such as chlorinated solvents (chloroform and dichloromethane).
    4. Discuss your proposed calibration method with your group. Specifically, discuss whether you think an internal standard should be used in calibration, and justify your response using evidence from analytical principles and the literature. Please consider the limitation that deuterated analytes are typically expensive.
    5. Write detailed protocols for sample extraction and calibration strategy in your notebook to prepare for the wet-lab session.

    🧪 Wet-Lab Agenda:

    1. Lessons and Demonstrations: Your TA will give a short lesson about the instrument you will be using for analysis. Draw diagrams of the instruments and equiptment in your notebook.
      • Instrument: Draw a diagram of the instrument components in your lab notebook.  Include and label the autosampler, sample, injector, the components of the chromatography system, and the components of the mass spectrometer.
      • Syringe-Driven Filter: Draw the syringe driven filter device in your notebook. 
      • Autosampler vials: Draw a diagram of the autosampler vial.
    2. Sample Preparation: Confirm that all group memebrs have the same plan for sample extraction. Record any observations and deviations from the planned protocol in your notebook and perform the sample extraction.
    3. Instrument method: Choose or write an appropriate method for analysis of your samples. Record the details of the instrument settings in your notebook. 
    4. Prepare sequence for sample injection. Use the instructions in the instrument protocol to create a sequence file to inject the following:
      • A blank (the solvent matrix of your samples)
      • Sample(s)
      • A standard mixture 
    5. Group discussion about electron ionization mass spectrometry. (while waiting for samples to run)
      • Search for cocaine mass spectrum using the NIST WebBook. 
      • Identify mass ion (303), and two most abundant fragment ions (82, 182) of cocaine.
      • Explain how electron ionization created the mass ion and the fragment ions (all are z=1).
    6. Prepare sequence for injection of calibration standards to run overnight.
    7. Export qualitative data figures and report.
      • Create a table that lists the compounds found, their mass ions, retention times, and confidence in the assignments. An example table is below.
        Example Table: ​​

    Compound

    Ions identified

    Found r.t. in standard (min)

    Found r.t. in sample (min)

    Confidence in compound identification

    exampleamine

    42, 84

    3.42

    3.43

    94%

    examplone

    54, 154, 187

    5.43

    5.42

    85%

    methylexample

    56, 74

    Not present

    4.38

    80%

    📘 Notebook

    Record detailed notes about your lab work in your notebook each time you are in lab. Also include the data analysis and responses to the reflection prompts*. Your notebook should be submitted on canvas prior to leaving Wet Lab each week - whatever state it is in at the end of lab is the state in which you should submit your work.  If you are unable to complete data analysis and the reflection prompt within the period, it should be completed before the next lab period, and submitted with your next notebook submission.

    Reflection Prompt \(\PageIndex{ }\) 

    1. Briefly describe the extraction procedure your group developed. Explain the reasoning behind your choices, including how these choices can be justified using chemical principles and/or literature sources.  

    2. Justify your group’s decision about whether to use an internal standard in your analysis. If you chose to use one, explain how its chemical properties make it appropriate for this experiment. Support your reasoning using relevant chemical principles (e.g., structural similarity, retention time, ionization efficiency, or extraction behavior).

    *Reflection prompts should be addressed in your lab notebook and should be included with the lab notebook submission. 

    ​​​​​​© 2026 Kathryn L. Haas and Jack Malek · CC BY-NC-SA 4.0

    This page titled 3.2: Week 1 - Money was last modified on Tue, 06 Oct 2026 12:46:01 GMT and is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by Kathryn Haas.