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Gas Chromatography. Gas Chromatograph: an overview ä What is chromatography ä History of chromatography ä Applications ä Theory of operation ä Detectors.

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Presentation on theme: "Gas Chromatography. Gas Chromatograph: an overview ä What is chromatography ä History of chromatography ä Applications ä Theory of operation ä Detectors."— Presentation transcript:

1 Gas Chromatography

2 Gas Chromatograph: an overview ä What is chromatography ä History of chromatography ä Applications ä Theory of operation ä Detectors ä Syringe technique ä What is chromatography ä History of chromatography ä Applications ä Theory of operation ä Detectors ä Syringe technique

3 stationary bed fluid What is Chromatography ä color writing ä the separation of mixtures into their constituents by preferential adsorption by a solid (Random House College Dictionary, 1988) ä Chromatography is a physical method of separation in which the components to be separated are distributed between two phases, one of the phases constituting a ______________ of large surface area, the other being a ______ that percolates through or along the stationary bed. (Ettre & Zlatkis, 1967, The Practice of Gas Chromatography) ä color writing ä the separation of mixtures into their constituents by preferential adsorption by a solid (Random House College Dictionary, 1988) ä Chromatography is a physical method of separation in which the components to be separated are distributed between two phases, one of the phases constituting a ______________ of large surface area, the other being a ______ that percolates through or along the stationary bed. (Ettre & Zlatkis, 1967, The Practice of Gas Chromatography)

4 History of Chromatography ä Mikhail Tswett separated plant pigments using paper chromatography ä liquid-solid chromatography ä 1930s - Schuftan & Eucken use vapor as the mobile phase ä gas solid chromatography ä Mikhail Tswett separated plant pigments using paper chromatography ä liquid-solid chromatography ä 1930s - Schuftan & Eucken use vapor as the mobile phase ä gas solid chromatography

5 gas Applications ä Compound must exist as a ____ at a temperature that can be produced by the GC and withstood by the column (up to 450°C) ä Alcohols in blood ä Aromatics (benzene, toluene, ethylbenzene, xylene) ä Flavors and Fragrances ä Permanent gases (H 2, N 2, O 2, Ar, CO 2, CO, CH 4 ) ä Hydrocarbons ä Pesticides, Herbicides, PCBs, and Dioxins ä Solvents ä Compound must exist as a ____ at a temperature that can be produced by the GC and withstood by the column (up to 450°C) ä Alcohols in blood ä Aromatics (benzene, toluene, ethylbenzene, xylene) ä Flavors and Fragrances ä Permanent gases (H 2, N 2, O 2, Ar, CO 2, CO, CH 4 ) ä Hydrocarbons ä Pesticides, Herbicides, PCBs, and Dioxins ä Solvents

6 Advantages of Gas Chromatography ä Requires only very small samples with little preparation ä Good at separating complex mixtures into components ä Results are rapidly obtained (1 to 100 minutes) ä Very high precision ä Only instrument with the sensitivity to detect volatile organic mixtures of low concentrations ä Equipment is not very complex (sophisticated oven) ä Requires only very small samples with little preparation ä Good at separating complex mixtures into components ä Results are rapidly obtained (1 to 100 minutes) ä Very high precision ä Only instrument with the sensitivity to detect volatile organic mixtures of low concentrations ä Equipment is not very complex (sophisticated oven)

7 Chromatogram of Gasoline 1. Isobutane 2. n-Butane 3. Isopentane 4. n-Pentane 5. 2,3-Dimethylbutane 6. 2-Methylpentane 7. 3-Methylpentane 8. n-Hexane 9. 2,4-Dimethylpentane 10. Benzene Methylhexane Methylhexane 13. 2,2,4-Trimethylpentane 14. n-Heptane 15. 2,5-Dimethylhexane 16. 2,4-Dimethylhexane 17. 2,3,4-Trimethylpentane 18. Toluene 19. 2,3-Dimethylhexane 20. Ethylbenzene 21. m-Xylene 22. p-Xylene 23. o-Xylene

8 Theory of Operation ä Velocity of a compound through the column depends upon affinity for the stationary phase Area under curve is ______ of compound adsorbed to stationary phase Gas phase concentration Carrier gas mass

9 Process Flow Schematic Carrier gas (nitrogen or helium) Sample injection Long Column (30 m) Detector (flame ionization detector or FID) Hydrogen Air

10 Gas Chromatograph Components Flame Ionization Detector Column Oven Injection Port top view front view

11 Flame Ionization Detector Hydrogen Air Capillary tube (column) Platinum jet Collector Sintered disk Teflon insulating ring Flame Gas outlet Coaxial cable to Analog to Digital converter Ions Why do we need hydrogen?

12 Flame Ionization Detector ä Responds to compounds that produce ____ when burned in an H 2 -air flame ä all organic compounds ä Little or no response to (use a Thermal Conductivity Detector for these gases) ä CO, CO 2, CS 2, O 2, H 2 O, NH 3, inert gasses ä Linear from the minimum detectable limit through concentrations ____ times the minimum detectable limit ä Responds to compounds that produce ____ when burned in an H 2 -air flame ä all organic compounds ä Little or no response to (use a Thermal Conductivity Detector for these gases) ä CO, CO 2, CS 2, O 2, H 2 O, NH 3, inert gasses ä Linear from the minimum detectable limit through concentrations ____ times the minimum detectable limit ions 10 7

13 Gas Chromatograph Output time (s) detector output ä Peak ____ proportional to mass of compound injected ä Peak time dependent on ______ through column ä Peak ____ proportional to mass of compound injected ä Peak time dependent on ______ through column area velocity

14 Other Detectors ä Thermal Conductivity Detector ä Difference in thermal conductivity between the carrier gas and sample gas causes a voltage output ä Ideal carrier gas has a very ____ thermal conductivity (He) ä Electron Capture Detector ä Specific for halogenated organics ä Thermal Conductivity Detector ä Difference in thermal conductivity between the carrier gas and sample gas causes a voltage output ä Ideal carrier gas has a very ____ thermal conductivity (He) ä Electron Capture Detector ä Specific for halogenated organics low

15 Advantage of Selective Detectors methane TCE time FID output ECD output Mixture containing lots of methane and a small amount of TCE

16 Gas chromatograph Mass Spectrophotometer ä Uses the difference in mass-to-charge ratio (m/e) of ionized atoms or molecules to separate them from each other. ä Molecules have distinctive fragmentation patterns that provide structural information to identify structural components. ä The general operation of a mass spectrometer is: ä create pure gas-phase ions ( __________________ ) ä separate the ions in space or time based on their mass- to-charge ratio ä measure the quantity of ions of each mass-to-charge ratio ä Uses the difference in mass-to-charge ratio (m/e) of ionized atoms or molecules to separate them from each other. ä Molecules have distinctive fragmentation patterns that provide structural information to identify structural components. ä The general operation of a mass spectrometer is: ä create pure gas-phase ions ( __________________ ) ä separate the ions in space or time based on their mass- to-charge ratio ä measure the quantity of ions of each mass-to-charge ratio

17 Mass Spec Output ä Each peak of a chromatogram becomes a fingerprint of the compound ä The fingerprints are compared with a library to identify the compounds ä Each peak of a chromatogram becomes a fingerprint of the compound ä The fingerprints are compared with a library to identify the compounds mass-to-charge ratio

18 Purge and Trap ä Way to measure dilute samples by concentration of constituents ä Trap constituents under low temperature ä Heat trap to release constituents and send to GC column ä Way to measure dilute samples by concentration of constituents ä Trap constituents under low temperature ä Heat trap to release constituents and send to GC column N2N2 N2N2 Trap

19 Techniques to Speed Analysis ä Problem: some components of a mixture may have very high velocities and others extremely low velocities. ä slow down fast components so they can be separated ä speed up slow components so analysis doesnt take forever ä Solution… ä Problem: some components of a mixture may have very high velocities and others extremely low velocities. ä slow down fast components so they can be separated ä speed up slow components so analysis doesnt take forever ä Solution…

20 Temperature Control Options Column: Petrocol DH, 100m x 0.25mm ID, 0.5µm film Cat. No.: U Oven: 35°C (15 min) to 200°C at 2°C/min, hold 5 min Carrier: helium, 20cm/sec (set at 35°C) Det.: FID, 250°C Inj.: 0.1µL premium unleaded gasoline, split (100:1), 250°C Example Method


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