05 Gas Chromatography - V Gas Chromatography CHM 614/714...

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V. Gas Chromatography CHM 614/714 Fall 2011
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In GC: Mobile phase is a gas. Stationary phase is usually a non-volatile liquid on a solid support, but sometimes a solid. Solute must be low molecular mass ( 450 amu ) gas or volatile liquid , and thermally stable.
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The most common form of gas chromatography is called gas-liquid partition chromatography (GLC). A viscous, non-volatile liquid coated on fine particles of an "inert" solid support is the stationary phase; P 0 5 mmHg at the vapor 0.5 mmHg at the column T. Ability to generate chemical selectivity through the choice of liquid phase. Occasionally, gas-solid adsorption chromatography Occasionally, gas solid adsorption chromatography (GSC) is used. In this case, the solid adsorbent is the stationary phase. Commonly, it can be silica, activated carbon, porous polymers, etc. It is most applicable for natural gases and other low-boiling point compounds .
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Instrumentation A schematic diagram of a gas chromatograph is shown as follows:
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A volatile liquid sample is injected through a rubber septum (a thin disk) into a heated glass injector port , which vaporizes the sample. G l b i j t d b ti ht i th h Gaseous samples can be injected by gas-tight syringe or through a gas-sampling valve. Th l i t th h th l b i t i The sample is swept through the column by an inert carrier gas (usually He, N 2 , or H 2 ), which serves as the mobile phase . The choice of carrier gas depends on the detector and desired separation efficiency and speed efficiency and speed. After passing through the column containing the stationary phase, the separated solutes flow through a detector whose response is separated solutes flow through a , whose response is displayed on a recorder or computer . The column temperature need not be above the boiling point of all The need not be above the boiling point of all solutes. It must only be hot enough for each solute to have sufficient vapor pressure to be eluted in a reasonable time. The detector is maintained at a higher temperature than the column, so that all solutes are gaseous in this chamber.
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The block diagram of a gas chromatograph:
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