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Gas and Supercritical Fluid Chromatography Lecture Date: April 7th, 2008 Gas and Supercritical Fluid Chromatography  Outline – Brief reviewof theory – Gas Chromatography – SupercriticalFluid Extraction – SupercriticalFluid Chromatography  Reading (Skoog et al.) – Chapter 27, Gas Chromatography – Chapter 29, Supercritical Fluid Chromatography  Reading (Cazes et al.) – Chapter 23, Gas Chromatography – Chapter 24, Supercritical Fluid Chromatography 1 GC and SFC: Very Basic Definitions  Gas chromatography – chromatography using a gas as the mobile phase and a solid/liquidas a stationary phase – In GC, the analytes migrate in the gas phase, so their boilingpoint plays a role – GC is generally applicable to compounds with masses up to about 500 Da and with ~60 torr vapor pressure at room temp (polar functional groups are trouble)  Supercriticalfluid chromatography – chromatography using a supercriticalfluid as the mobile phase and a solid/liquidas a stationary phase – In SFC, the analytes are solvated in the supercritical fluid – SFC is applicableto a much wider range of molecules Review of Chromatography  Important concepts/equations to remember: Selectivity: Retention volume:  = KB / KA V = tF  Column/separation performance: Plates: N = L/H  Linear velocity of mobile phase: u = L/tm 2 Review of Chromatography  Terminology and equations from Skoog: GC Theory  Mobile-phase flow rates are much higher in GC (pressure drop is much less for a gas)  The effect of mobile-phase flow rate on the plate height (H) is dramatic – Lower plate heights yield better chromatography – However, much longer columns can be used with GC 3 GC Instrumentation  Basic layout of a GC: Injector Detector Carrier Gas Column Oven  See pg 703 of Skoog et al. for a similar diagram GC Instrumentation  Atypical modern GC – the Agilent 6890N: Diagram from Agilent promotional literature. 4 GC Instrumentation  Typical carrier gases (all are chemically inert): helium, nitrogen and hydrogen. The choice of gas affects the detector.  Injectors: most desirable to introduce a small “plug”, volatilizethe sample evenly – Most samples introduced in solution: microflashinjections “instantly” volatilizethe solvent and analytes and sweep them into the column  Splitters: effectively dilute the sample, by splitting off a portion of it (up to 1:500)  Ovens: Programmable, temperature ranges from 77K (LN2) up to 250 C.  Detectors: wide variety, to be discussed shortly… Headspace GC  Avery useful method for analyzing volatiles present in non-volatilesolids and liquids  Sample is equilibratedin a sealed container at elevated temperature Needle Headspace  The “headspace” in the container is sampled and introduced into a GC Liquid/solid 5 ... - tailieumienphi.vn
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