CHEM 5181, Fall 2006
Laboratory #2
Dates: October 9-12, 2006
Reports Due: October 31, 2006 (start of class)
During the first 30 minutes, you will be given the information you need to use the GCMS: How to check the background in the mass spectrometer, how to run a sample, how
to “play” with the data and finally how to use the NIST library (this part could be very
useful for part #5).
You will be provided with 3 solutions A, B and C. Solutions A and B contain just one
compound in methanol and solution C is a mixture of 5 compounds in methanol.
Directions:
1. Before you use the GC-MS you should be sure that you don’t have a leak.
Use the ratios 18/28, 28/32 and the ionization time to evaluate your system.
2. Inject 1 l of solution A with the method chemMS.
Search the spectrum against the NIST database.
What’s the compound?
Try to interpret the major fragments.
3. Inject 1 l of solution A with the method chemMS2 (MS/MS on fragments 194 and
109). Print MS/MS spectrum of ions 194 and 89.
4. Inject 1 l of solution B with the method chemMSsplitless
Inject 1 l of solution B with the method ChemMS_SIM_splitless
Inject 1 l of solution B with the method ChemMSMS_SIM_splitless
Explain the difference between these 3 methods. If you have to analyze the same
compound at a trace level in a complex mixture, which method you should use? What’s
the compound in solution B? (Justify your answers).
5. Inject 1 l of solution C with Chem2MS.
Give the retention time and the major fragments of all compounds in the solution.
Often people derivatize their mixture (ex: silylation with N,O-Bis(trimetylSilyl)TriFluoroAcetamid, BSTFA). What’s the general idea behind the
derivatization? Why we didn’t derivatize mixture C?