Gas Chromatography


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A complete presentation on gas chromatography, illustrating the basics, operation and different instrumentation components of the whole system.
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Gas Chromatography

  2. 2. • Principles Partition of molecules between gas (mobile phase) and liquid (stationary phase). Gas Liquid Chromatography
  3. 3. Most Common Stationary Phases 1. Separation of mixture of polar compounds Carbowax 20M (polyethylene glycol) 2. Separation of mixtures of non-polar compounds OV101 or SE-30 (polymer of methylsilicone) 3. Methylester of fatty acids DEGS (diethylene glycol succinate)
  4. 4. Filters/Traps Air Hydrogen GasCarrier Column Gas Chromatography • gas system • inlet • column • detector • data system Data system Syringe/Sampler Inlets Detectors Regulators H RESET
  5. 5. Schematic Diagram of Gas Chromatography
  6. 6. Detector • Flame Ionization Detector (Nanogram - ng) High temperature of hydrogen flame (H2 +O2 + N2 ) ionizes compounds eluted from column into flame. The ions collected on collector or electrode and were recorded on recorder due to electric current.
  7. 7. Exhaust Chimney Igniter Hydrogen Inlet Column Effluent Collector Electrode Schematic Diagram of Flame Ionization Detector
  8. 8. Measures the changes of thermal conductivity due to the sample (µg). Sample can be recovered. Thermal Conductivity Detector
  9. 9. Thermal Conductivity Detector Principal: The thermal balance of a heated filament Electrical power is converted to heat in a filament and the temperature will climb until heat power loss form the filament equals the electrical power input. The filament may loose heat by radiation to a cooler surface by conduction to the molecules which contact with the filament.
  10. 10. Thermal Conductivity Basics When the carrier gas is contaminated by sample , the cooling effect of the gas changes. The difference in cooling is used to generate the detector signal. The TCD is a nondestructive, concentration sensing detector. A heated filament is cooled by the flow of carrier gas. Flow Flow
  11. 11. When a separated compound elutes from the column , the thermal conductivity of the mixture of carrier gas and compound gas is lowered. The filament in the sample column becomes hotter than the control column. The imbalance between control and sample filament temeprature is measured by a simple gadget and a signal is recorded Thermal Conductivity Detector
  12. 12. Relative Thermal Conductivity Compound Relative Thermal Conductivity Carbon Tetrachloride 0.05 Benzene 0.11 Hexane 0.12 Argon 0.12 Methanol 0.13 Nitrogen 0.17 Helium 1.00 Hydrogen 1.28
  13. 13. Thermal Conductivity Detector
  14. 14. • Responds to all compounds • Adequate sensitivity for many compounds • Good linear range of signal • Simple construction • Signal quite stable if carrier gas glow rate, block temperature, and filament power are effectively controlled • Nondestructive detection Thermal Conductivity Detector
  15. 15. Electron Capture Detector Analyses for pesticide, Insecticides, vinyl chloride, and fluorocarbons in foods. Most sensitive detector (10-12 gram)
  16. 16. Electron Capture Detector ECD detects positive ions of carrier gas by the anode electrode. 63 Ni emits β particles. Ionization : N2 (Carrier gas) + β (e) = N2 + + 2e. The N2 + establish a “base line” X (F, Cl and Br) containing sample + β (e)  X- Ion recombination: X- + N2 + = X + N2, The “base line” due to the N2 + will decrease and this decrease constitutes the signal. The more the halogen containing X compounds in the sample, the less the N2 + in the detector
  17. 17. Electron Capture Detector
  18. 18. Electron Capture Detector
  19. 19. Chromatogram of Compounds from Fermented Cabbage
  20. 20. Chromatogram of Orange Juice Compounds
  21. 21. Gas Chromatography Application
  22. 22. Semi-Quantitative Analysis of Fatty Acids C C C DetectorResponse Retention Time 14 16 18 PeakArea Sample Concentration (mg/ml) 2 4 6 8 10 0.5 1.0 1.5 2.0 2.5 3.0 The content % of C fatty acids = C C + C + C 100∗ 14 181614 = the content % of C fatty acids14 14
  23. 23. Tentative Identification of Unknown Compounds Response GC Retention Time on Carbowax-20 (min) Mixture of known compounds Hexane Octane Decane1.6 min = RT Response Unknown compound may be Hexane 1.6 min = RT Retention Time on Carbowax-20 (min)
  24. 24. Response GC Retention Time on SE-30 Unknown compound RT= 4 min on SE-30 Response GC Retention Time on SE-30 Hexane RT= 4.0 min on SE-30 Retention Times
  25. 25. Advantages of Gas Chromatography • Very good separation • Time (analysis is short) • Small sample is needed - µl • Good detection system • Quantitatively analyzed
  26. 26. Disadvantages of Gas Chromatography Material has to be volatilized at 250C without decomposition. R C OH CH3OH H2SO4 O R C O CH3 O CH2 O C R CH O C R CH2 O C R O O O CH3OH O R C O CH3 CH3ONa Fatty Acids Methylester Reflux + 3 Volatile in Gas Chromatography Volatile in Gas Chromatography + +
  27. 27. Gas Chromatogram of Methyl Esters of Fatty Acids
  28. 28. Effects of OH groups of Carbohydrates OH O OH OH HO CH 2 OH 1 23 4 5 6
  29. 29. OH O OH OH HO CH2 OH 1 23 4 5 6 + Si CH3 CH3 CH35Cl O-Si(CH3)3 O O-Si(CH3)3 O-Si(CH3)3 (CH3)3-Si-O CH2 O-Si(CH3)3 1 23 4 5 6 5HCl+ Derivation of Glucose with Trimethylchlorosilane Glucose Trimethylchlorosilane
  30. 30. Effects of Derivation • Time consumption • Side reaction • Loss of sample
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