05 Gas Chromatography

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

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V. Gas Chromatography HM 614/714 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 upport is the stationary phase; P 5 mmHg at the support is the stationary phase; P vapor 0.5 mmHg at the column T. Ability to generate chemical selectivity through the choice of liquid phase. qp ccasionally, as- olid 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: gg g p
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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. Gaseous samples can be injected by gas-tight syringe or through a gas-sampling valve. 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 fficiency and speed efficiency and speed. After passing through the column containing the stationary phase, the eparated solutes flow through a etector whose response is separated solutes flow through a detector , whose response is displayed on a recorder or computer . he olumn temperature eed not be above the boiling point of all The column temperature 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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Column 1) Packed columns made of stainless steel or glass typically 3-6 mm in diameter and 1-5 m in length. The column filled with a fine solid support (~150 m in diameter) coated with a nonvolatile liquid stationary phase, or the solid may be the stationary phase. For preparative purposes, the thickness of the stationary phase is creased so that more sample can be accommodated and rger increased so that more sample can be accommodated, and larger diameter columns are preferred. With a 5-m column , a maximum efficiency of 10,000 plates can be reached. The back pressure is the main reason that prevent the use f longer column. of longer column.
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2) Open tubular (capillary) columns. Open tubes with 0.10 to 0.53 m i d he stationary phase is coated on the inside capillary walls mm i.d. The stationary phase is coated on the inside capillary walls.
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This note was uploaded on 10/20/2011 for the course CHEM 653 taught by Professor Wei, robert during the Spring '11 term at Cleveland State.

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

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