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Gases
C H A P T E R 1 8
GASES
18.1. GC SEPARATIONS A. Capillary columns 1. Oxygen, nitrogen, methane, and carbon monoxide 25-m Molecular Sieve 5A Plot column at room temperature. (Note: This column separates oxygen and nitrogen better than the Molecular Sieve 13X column; neither column separates argon and oxygen.) 2. Nitrous oxide, carbon dioxide, and nitric oxide 25-m GS-Q column or 25-m Poraplot Q column at room temperature. 3. Air, carbon monoxide, methane, and carbon dioxide
25-m Carboplot OO7 column at 60 °C.
4. Carbon dioxide, carbonyl sulfide, hydrogen cyanide, propylene, and butadiene 25-m GS-Q column or 25-m Poraplot Q column, 60–200 °C at 6 °C min�1. 5. Methane, carbon dioxide, ethylene, propylene, and propane
25-m Poraplot R column, 30–100 °C at 5 °C min�1.
6. Methane, ethane, ethylene, propane, propylene, acetylene, isobutane, and n-butane 25-m Poraplot Alumina column, 35–140 °C at 6 °C min�1. 7. Air, hydrogen sulfide, carbonyl sulfide, sulfur dioxide, methyl mercaptan, and carbon disulfide 25-m GS-Q column or 25-m Poraplot Q column, 60–200 °C at 8 °C min�1. 8. CHF3, CH2F2, CH3CF3, CHF2Cl, CF2Cl2, CH2FCl, CHF2CH2Cl, and CHFCl2 25-m Poraplot Q column, 60–150 °C at 5 °C min�1.
18.2. GENERAL INFORMATION A gas analysis usually involves some or all of the common gases: O2, N2,
CO, CO2, C1–C5 hydrocarbons, low-boiling fluorinated compounds,
Gas Chromatography and Mass Spectrometry DOI: 10.1016/B978-0-12-373628-4.00018-6
� 2010 by Academic Press. Inc. All rights reserved.
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sulfur compounds, and so forth. Separating or passing the eluate from the GC column through a sensitive thermal conductivity detector (TCD) before entering the mass spectrometer enables the qualitative and quantita tive analyses of unknown gas mixtures from parts per million to percentage levels. If elaborate column switching systems are not available, two GC/MS analyses may be required on two different GC columns. For instance, CO2 and the C2–C5 hydrocarbons are adsorbed on the Molecular Sieve 5A column while separating H2, O2, N2, CH4, and CO. A second GC/MS analysis is performed using GS-Q or Poraplot Q, which separates CO2 and the C2–C5 hydrocarbons from composite peaks of H2, O2, N2, CH4, and CO. By performing two GC/MS analyses on two different columns, a complete gas analysis can be achieved. Remember that if a sufficient number of analyses are made, the Molecular Sieve 5A column will have to be replaced.
GASES
18.1. GC SEPARATIONS A. Capillary columns 1. Oxygen, nitrogen, methane, and carbon monoxide 25-m Molecular Sieve 5A Plot column at room temperature. (Note: This column separates oxygen and nitrogen better than the Molecular Sieve 13X column; neither column separates argon and oxygen.) 2. Nitrous oxide, carbon dioxide, and nitric oxide 25-m GS-Q column or 25-m Poraplot Q column at room temperature. 3. Air, carbon monoxide, methane, and carbon dioxide
25-m Carboplot OO7 column at 60 °C.
4. Carbon dioxide, carbonyl sulfide, hydrogen cyanide, propylene, and butadiene 25-m GS-Q column or 25-m Poraplot Q column, 60–200 °C at 6 °C min�1. 5. Methane, carbon dioxide, ethylene, propylene, and propane
25-m Poraplot R column, 30–100 °C at 5 °C min�1.
6. Methane, ethane, ethylene, propane, propylene, acetylene, isobutane, and n-butane 25-m Poraplot Alumina column, 35–140 °C at 6 °C min�1. 7. Air, hydrogen sulfide, carbonyl sulfide, sulfur dioxide, methyl mercaptan, and carbon disulfide 25-m GS-Q column or 25-m Poraplot Q column, 60–200 °C at 8 °C min�1. 8. CHF3, CH2F2, CH3CF3, CHF2Cl, CF2Cl2, CH2FCl, CHF2CH2Cl, and CHFCl2 25-m Poraplot Q column, 60–150 °C at 5 °C min�1.
18.2. GENERAL INFORMATION A gas analysis usually involves some or all of the common gases: O2, N2,
CO, CO2, C1–C5 hydrocarbons, low-boiling fluorinated compounds,
Gas Chromatography and Mass Spectrometry DOI: 10.1016/B978-0-12-373628-4.00018-6
� 2010 by Academic Press. Inc. All rights reserved.
317
318
Chapter 18
sulfur compounds, and so forth. Separating or passing the eluate from the GC column through a sensitive thermal conductivity detector (TCD) before entering the mass spectrometer enables the qualitative and quantita tive analyses of unknown gas mixtures from parts per million to percentage levels. If elaborate column switching systems are not available, two GC/MS analyses may be required on two different GC columns. For instance, CO2 and the C2–C5 hydrocarbons are adsorbed on the Molecular Sieve 5A column while separating H2, O2, N2, CH4, and CO. A second GC/MS analysis is performed using GS-Q or Poraplot Q, which separates CO2 and the C2–C5 hydrocarbons from composite peaks of H2, O2, N2, CH4, and CO. By performing two GC/MS analyses on two different columns, a complete gas analysis can be achieved. Remember that if a sufficient number of analyses are made, the Molecular Sieve 5A column will have to be replaced.