RelativeResourceManager(14) - Gas chromatography Chem 420...

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Gas chromatography Chem 420 October 22, 2008 Professor Ryan C. Bailey
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Problem Set #3 z Posted on Compass. z Due in class on October 29 z Note: This is two days later than the syllabus states. z Assignments are due at beginning of class—starts at 12 Noon! z For full credit assignments must be in box when the lecture begins. z Any assignment turned in between noon and 12:05 PM will automatically be deducted 5 points. z Assignments will NOT be accepted for credit after 12:05 PM. z Score = 0
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Recap from last class z What is chromatography? z How does it work? What are the underlying principles? z What determines migration rate? z Don’t directly measure partition coefficient but can measure retention time, which is related. z How is column efficiency defined? z Band broadening can be described by what equation? z What are the factors involved? z What metric addressed the ability to observe one peak independent of another? z See Example 26-1 in Skoog ZZZX YZZZ c K mobile stationary stationary c mobile AA c K c = RM A M tt k t ( ) () α = B A = L N H 2 16 ⎛⎞ = ⎜⎟ ⎝⎠ R t N W =+ + + sM B HA C u C u u ( ) ( ) 2 RR BA s AB R WW W ⎡⎤ ⎣⎦ == + 1 41 B s B k N R k = +
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Questions?
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Gas chromatography z Gas-liquid chromatography (aka gas chromatography) z Stationary phase is solid support (column walls or particles) coated by a liquid partition layer. z Gas-solid chromatography (we won’t discuss in more detail) z Stationary phase is a solid support and separation is achieved by differential adsorption. z Adsorption is non-linear process and polar molecules can be irreversibly bound. z Observed as severe tailing z Not commonly used except for low-molecular-mass gaseous species
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van Deemter considerations in gas chromatrography z van Deemter relationship, discussed on 10/20, holds for GC. z Of note, the B/u term is more significant for GC because of much higher (10 4 -10 5 times) diffusion rates in the gas phase. z Result: Broader minima in van Deemter plot. =+ + + sM B HA C u C u u
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Basic instrumental setup for GC Carrier gas system: • Chemically inert gas (often He) • Pressure regulators •F low me te r Sample injection system: • Goal is to introduce “plug” •Not too big or slow • Calibrated microsyringes •10 -1 -20 mL for regular column •100-fold smaller for capillary columns (requires splitter) • Heated sample port instantly vaporizes liquid samples Will discuss later
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This note was uploaded on 04/08/2010 for the course CHEM 420 taught by Professor Bailey during the Spring '08 term at University of Illinois at Urbana–Champaign.

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RelativeResourceManager(14) - Gas chromatography Chem 420...

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