Pre-Lab Worksheet
Gas Chromatography/Mass Spectrometry Lab Week of 11/27/06
(You need to bring your laptops for this lab!!!!)
- Read through http://www.scientific.org/tutorials/articles/gcms.html
This website will be helpful in answering some of the following questions.
- Define chromatography
- Give a brief explanation of gas chromatography
- Give a brief description of mass spectrometry
- What are some applications for Gas Chromatography/Mass Spectrometry?
- Go to the Virtual Mass Spectrometry Laboratory (http://mass-spec.chem.cmu.edu/VMSL and save as a favorite on your laptop. Describe the purpose of Virtual Mass Spectrometry Laboratory and list who funded this effort.
- At the VMSL, read through Current Case Study on Cocaine Analysis in Hair
GC/MS Exploration Lab
**There will be a lab test at the end of lab to quiz you on the concepts from the prelab questions and also from the experiments conducted in lab today. Each of you should take notes in your lab notebook and ask questions if you do not understand a concept.
Section 1: Understanding spectra from the NIST (National Institute of Standards and Technology) library
1) Before going to the NIST spectra go to www.sigmaaldrich.com and get the molecular weight of each compound, density, molecular formula, and draw structure if given. Go to a Computer with the Mass Spectral Library. Identify the numbered peaks by what atom(s) would have to be lost to give the ion mass/charge observed.
Hydrazine
Bis(2-chloroethyl)methylamine (not the hydrochloride)
Oleyl Alcohol
Section 2: Get the data for the cocaine standard and for a $20 bill, $5 and a $1 washed with ethanol (files)
Determine if cocaine is present on the money and explain how you came about your decision.
Section 3: Analyze the unidentified mass spectra and generate a best guess structure for the compound. Show your reasoning for the atoms that you choose.
Section 4: Run a 5.0 x 10-4 M solution of an assigned known and the unknown mixture (Go to Rm 306 by the instrument). Start your samples then:
Go to www.sigmaaldrich.com and get the molecular weight of the assigned known compound, density, molecular formula, and draw structure if given.
While the samples are running complete the following calculation in your notebook: If 10 uL of known (use your assigned known, remember that density is important here) is added to 2mL to prepare the stock solution what is the concentration (M). How many uL of the stock standard should you use if made up a 2.0 mL solution at 5.0 x 10-4 M.
Remember that M1V1=M2V2 is used for dilutions.
Group
|
Assigned unknown
|
Assigned known
|
Group 1
|
Unknown mix 1
|
chlorophenol
|
Group 2
|
Unknown mix 1
|
bromobenzene
|
Group 3
|
Unknown mix 2
|
chlorophenol
|
Group 4
|
Unknown mix 2
|
bromobenzene
|
Group 5
|
Unknown mix 3
|
chlorophenol
|
Group 6
|
Unknown mix 3
|
bromobenzene
|
Section 5: Look up the isotopes for chlorine and bromine and find their natural abundances. Use your mass spectra of chlorophenol and bromobenzene to check these natural abundances. Determine the ratio of isotopes for the halogenated compounds using your molecular ions from the data you and other groups have collected. Are both isotopes observed? Are they in the correct ratios?
Analyze your unknown mixture to determine what compounds were in the mixture. What percentage certainty do you have for your results? This may be easiest if you make a table and list unknown compound, SI and RSI.
Section 6: Complete GC/MS Quiz
Post-Lab Quiz
Gas Chromatography/Mass Spectrometry Lab Week of 11/27/06
1. What is an isotope and how does GC/MS distinguish between isotopes?
2. Give a brief explanation of gas chromatography and describe how it was used in this lab.
3. Give a brief description of mass spectrometry in terms of your unknown sample.
4. Describe the case about cocaine that you read at the VMSL. How is this cocaine case different than the cocaine experiment that you examined in the SFU lab? From Section 2 lab handout, what were your findings?
5. Discuss how your processed your unknown sample. What are the compounds that you found and what is the certainty in your answer (Give SI and RSI values). It may be easier to present this in Table form. Explain how you arrived at this conclusion.
6. Section 1 - Explain your finding for Hydrazine
7. Attach the worksheet for Section 3 with the molecular formula that you have determined.