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Gas chromatography . ppt
- 8. The Next Generation in Gas Chromatography
- 14. Peaks and Data
- 38. 1.Thermal Conductivity Detector (Katharometer, Hot Wire Detector) Measures the changes of thermal conductivity due to the sample ( g). Sample can be recovered.
- 39. 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
- 40. 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 temperature is measured by a simple gadget and a signal is recorded Thermal Conductivity Detector
- 43. Relative Thermal Conductivity 0.17 Nitrogen 0.13 Methanol 1.00 Helium 0.12 Argon Relative Thermal Conductivity Compound 1.28 Hydrogen 0.12 Hexane 0.11 Benzene 0.05 Carbon Tetrachloride
- 47. FID
- 61. Retention time
- 64. Resolution
- 65. Resolution
- 76. Gas Chromatography vials caps
- 80. Semi-Quantitative Analysis of Fatty Acids C C C Detector Response Retention Time 14 16 18 Peak Area Sample Concentration (mg/ml ) 2 4 6 8 10 0.5 1.0 1.5 2.0 2.5 3.0
- 81. Tentative Identification of Unknown Compounds Response GC Retention Time on Carbowax-20 (min) Mixture of known compounds Hexane Octane Decane 1.6 min = RT Response Unknown compound may be Hexane 1.6 min = RT Retention Time on Carbowax-20 (min)
- 82. Retention Times 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
Notas del editor
- Packed - As suggested by the term, it is filled with a coated inert solid support such as fire brick, alumina, and graphite with a specific mesh size. The coatings are called phases and for best results are chemically bonded to the support. Chemical bonding provides for longer column life and less bleeding (major source of background noise) contributing to lower sensitivity. Column dimensions 1/8” - 1/4” ID x up to about 6’ using glass or stainless steel. Advantages - higher capacity (higher conc). Disadvantages: low resolution and low S/N. Capillary - Here the phase (film) is coated on the inside diameter of the capillary wall with film thickness range of 0.1 to 5μ where the ticker film provides for better resolution but also allows for more bleed. Typical dimensions .25mm - .53mm ID x up to 60m made of fused silica coated with polyamide. Advantages: high resolution and better S/N. Disadvantages: low capacity and cost.
- Isothermal - Keep oven at one temp thru run. Not very useful. Possibly useful for series of very similar compounds differing by boiling points such as alcohols ( MeOH, EtOH, n-PrOH, i-PrOH, BuOH, i-BuOH). BP 64.6 78.3 97.2 82.4 117.6 99.5 Gradient - temp profile: 40 deg hold for 10 min then 10deg/min to 240 deg and hold there for 20 min. Advantages: 1- resolution and 2- analysis time.