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Gas chromatography = separation Mass spectrometry = detection

CH 103: ATOMIC MASS AND ISOTOPIC ABUNDANCE GAS CHROMATOGRAPHY MASS SPECTROMETRY. Gas chromatography = separation Mass spectrometry = detection. GAS CHROMATOGRAPHY. A gas chromatograph (GC) separates mixtures of 2 or more different chemicals into pure compounds. GAS CHROMATOGRAPHY.

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Gas chromatography = separation Mass spectrometry = detection

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  1. CH 103: ATOMIC MASS AND ISOTOPIC ABUNDANCE GAS CHROMATOGRAPHY MASS SPECTROMETRY • Gas chromatography = separation • Mass spectrometry = detection

  2. GAS CHROMATOGRAPHY • A gas chromatograph (GC) separates mixtures of 2 or more different chemicals into pure compounds.

  3. GAS CHROMATOGRAPHY • The sample is injected into the GC inlet where it is heated and swept onto a chromatographic column by a carrier gas. • The pure compounds in a mixture are separated by interacting with the coating or packing of the column (stationary phase) and the carrier gas (mobile phase). • This separation is often improved by programming changes in column temperature and pressure.

  4. GAS CHROMATOGRAPHY • Splitless Injection Animation • http://www.restek.com/info_animation_splitless.asp • Splitless injections direct the entire sample to the column. • 2 mL/min septum purge flow + 3 mL/min column flow = • 5 mL/min total flow • Unknowns might be analyzed with a 0.2 μL splitless injection to identify minor components.

  5. GAS CHROMATOGRAPHY • Split Injection Animation • http://www.restek.com/info_animation_split.asp • Split injections direct a fraction of the sample to the column and the remaining sample vents out of the GC. • 2 mL/min septum purge flow + 1 mL/min column flow + • 100 mL/min split flow = 103 mL/min total flow • Complicated mixtures, such as petroleum, might be analyzed with a 1.0 μL injection using a 1 to 100 split to identify major components.

  6. MASS SPECTROMETRY • A mass spectrometer (MS) determines the structure and quantity of each pure chemical leaving the GC. For example, the mass spectrum suggests that this compound is chloromethane (CH3Cl). The total abundance of the peak at m/z = 50 amu suggests that the concentration of CH3Cl is 150 parts per million (ppm).

  7. MASS SPECTROMETRY • The separated compounds leave the GC and enter the ion source in the MS where a beam of electrons ionize these molecules. This typically causes the loss of 1 electron from an ionized molecule and produces a radical cation called the molecular ion which has the same molecular weight as the original molecule.

  8. MASS SPECTROMETRY

  9. MASS SPECTROMETRY • The molecular ion usually fragments to produce smaller ions with characteristic relative abundances that provide a unique “fingerprint” for that molecular structure. These positively charged ions are filtered by the quadrupole of the mass selective detector. Finally, this fingerprint is shown as a mass spectrum.

  10. MASS SPECTROMETRY • Important peaks are 12C1H337Cl+. at m/z = 52 amu, 12C1H335Cl+. at m/z = 50 amu, and 12C1H3+. at m/z = 15 amu.

  11. MASS SPECTROMETRY • Important peaks are 12C1H237Cl37Cl+. at m/z = 88 amu, 12C1H235Cl37Cl+. at m/z = 86 amu, 12C1H235Cl35Cl+. at m/z = 84 amu, 12C1H237Cl+. at m/z = 51 amu, and 12C1H235Cl+. at m/z = 49 amu.

  12. MASS SPECTROMETRY • Important peaks are 12C1H381Br+. at m/z = 96 amu, 12C1H379Br+. at m/z = 94 amu, and 12C1H3+. at m/z = 15 amu.

  13. MASS SPECTROMETRY • Important peaks are 12C1H281Br81Br+. at m/z = 176 amu, 12C1H279Br81Br+. at m/z = 174 amu, 12C1H279Br79Br+. at m/z = 172 amu, 12C1H281Br+. at m/z = 95 amu, and 12C1H279Br+. at m/z = 93 amu.

  14. LIQUID CHROMATOGRAPHY MASS SPECTROMETRY Liquid Chromatography Mass Spectrometry Animation http://www.chem.agilent.com/Scripts/Generic.ASP?lPage=10184&indcol=N&prodcol=Y

  15. SOURCES • Agilent Technologies. 2006. Agilent. Available: http://www.home.agilent.com/agilent/home.jspx?cc=US&lc=eng&cmpid=4533 [accessed 1 September 2006]. • Agilent Technologies. 2006. 6210 Time-of-Flight LC/MS. Available: http://www.chem.agilent.com/Scripts/Generic.ASP?lPage=10184&indcol=N&prodcol=Y [accessed 1 September 2006]. • Bull I.D., P. Gates. 2005. Gas Chromatography Mass Spectrometry (GC/MS). Available: http://www.bris.ac.uk/nerclsmsf/techniques/gcms.html [accessed 1 September 2006]. • McLafferty, F.W. 1980. Interpretation of Mass Spectra, 3rd ed. Mill Valley, CA: University Science Books. • National Institute of Standards and Technology. 2006. NIST Chemistry WebBook. Available: http://webbook.nist.gov/chemistry/ [accessed 1 September 2006]. • Restek Corporation. 2006. Split Injection Animation. Available: http://www.restek.com/info_animation_split.asp [accessed 1 September 2006]. • Restek Corporation. 2006. Splitless Injection Animation. Available: http://www.restek.com/info_animation_splitless.asp [accessed 1 September 2006].

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