Lecture 34. Chromatography Pt3

Lecture 34. Chromatography Pt3 - Mass Transfer (C) Mass...

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Unformatted text preview: Mass Transfer (C) Mass broadening ∝ u Daniel C. Harris, Exploring Chemical Analysis, 2nd ed., W.H. Freeman and Company, New York, 2001. Freeman Eddy Diffusion (A) Eddy Independent of flow rate (u) Daniel C. Harris, Exploring Chemical Analysis, 2nd ed., W.H. Freeman and Company, New York, 2001. Freeman Liquid Phase Diffusion from a Plane Source Concentration vs Distance D = 1e-5 cm^2/s 1000 t = 0. 01s t = 0. 03s 500 Concentration 0 0. 000 Di sta nce (cm ) t = 0. 1s t = 0. 3s t = 1s -0. 010 -0. 005 0. 005 0. 010 Van Deemter Equation Van Optimizing flow rate (u) Gary D. Christian, Analytical Chemistry, 6th ed., John Wiley & Sons, Inc., U.S.A., 2004. 2004. Packed Columns are the Standard of HPLC HPLC Daniel C. Harris, Exploring Chemical Analysis, 2nd ed., W.H. Freeman and Company, New York, 2001. Freeman Packed Columns: Packed Reducing Particle Size Increases N Gary D. Christian, Analytical Chemistry, 6th ed., John Wiley & Sons, Inc., U.S.A., 2004. 2004. Chapter 22: Chromatography Chapter Gas Chromatography Daniel C. Harris, Exploring Chemical Daniel Analysis, 3rd ed., W.H. Freeman and Analysis, Company, New York, 2005. Company, Gary D. Christian, Analytical Chemistry, 6th ed., John Wiley & Sons, Inc., U.S.A., 2004. ed., GC Chromatogram GC Gary D. Christian, Analytical Chemistry, 6th ed., John Wiley & Sons, Inc., U.S.A., 2004. 2004. Gary D. Christian, Analytical Chemistry, 6th ed., John Wiley & Sons, Inc., U.S.A., Gary 2004. 2004. Types of Gas Chromatography Types Packed Column Open Columns Gary D. Christian, Analytical Chemistry, 6th ed., John Wiley & Sons, Inc., U.S.A., 2004. 2004. Open Tubular Columns Open Daniel C. Harris, Exploring Chemical Analysis, 3rd ed., W.H. Freeman and Company, New York, 2005. Freeman Stationary Phases Phases Gary D. Christian, Analytical Chemistry, 6th ed., John Wiley & Sons, Inc., U.S.A., 2004. 2004. Stationary Phase Affects α ( Separation Factor) Factor) Poly(dimethylsiloxane) Poly(ethylene glycol) Note: Alcohols are eluted much faster Note: than expected from their boiling points. Why? Why? Daniel C. Harris, Exploring Chemical Analysis, 3rd ed., W.H. Freeman and Company, New York, 2005. Freeman Effect of Temperature Effect Temperature Programming Daniel C. Harris, Exploring Chemical Analysis, 3rd ed., W.H. Freeman and Company, New York, 2005. Freeman GC Detectors GC Gary D. Christian, Analytical Chemistry, 6th ed., John Wiley & Sons, Inc., U.S.A., 2004. 2004. Resolution Resolution t R2 - t R1 Rs = (w b1 + w b2 )/ 2 Daniel C. Harris, Exploring Chemical Analysis, 2nd ed., W.H. Freeman and Company, New York, 2001. Freeman N big, α big N big, α small big, N small, α big small, N small, α small small, Factors That Factors Affect Resolution • # of Theoretical Plates (N) of N∝L • Retention Factor (k) Retention tR - tM tR ' κ= = tM tM • Separation Factor (α ) Separation t R2' k 2 α= = t R1' k1 Gary D. Christian, Analytical Chemistry, 6th ed., John Wiley & Sons, Inc., U.S.A., 2004. 2004. Chromatograms Chromatograms tM = Elution time of an unretained solute. tR = Retention time tR’ = Adjusted retention time wb = Peak width at baseline w1/2 = Peak width at half height Gary D. Christian, Analytical Chemistry, 6th ed., John Wiley & Sons, Inc., U.S.A., 2004. 2004. The examples shown here from liquid-solid chromatography (LSC). LLC The would not give such good separations because liquid-liquid distribution coefficients would not be as large. coefficients Separation Factor (α) Separation t R2' k 2 α= = t R1' k1 Interaction Interaction Ideal weaker weakest Time/min Stereoisomers are best Stereoisomers separated by LSC, not LLC. separated Silicagel has many polar Silicagel functional groups (OH, ether, Lewis acid sites). Lewis How Could You Improve These Separations? Separations? (A) Change the stationary and/or mobile phase to change α. (B) GC: Lower the temperature. RPLC: Use a more polar mobile (B) phase that give larger retention (k). phase (C) Use a column giving a higher number of theoretical plates (N). A Different Type of Chromatography: Size Exclusion Chromatography Size => Chem 4101 A Different Type of Chromatography: Ion Exchange Chromatography Ion => Chem 4101 A Different Type of Separation: Electrophoresis Electrophoresis => Chem 4101 High-Performance Liquid Chromatography (HPLC) (HPLC) Gary D. Christian, Analytical Chemistry, 6th ed., John Wiley & Sons, Inc., U.S.A., 2004. ed., Daniel C. Harris, Exploring Chemical Analysis, Daniel 3rd ed., W.H. Freeman and Company, New York, 2005. York, HPLC Columns HPLC Gary D. Christian, Analytical Chemistry, 6th ed., John Wiley & Sons, Inc., U.S.A., 2004. 2004. Packed Columns are the Standard of HPLC HPLC Daniel C. Harris, Exploring Chemical Analysis, 2nd ed., W.H. Freeman and Company, New York, 2001. Freeman HPLC Stationary Phases Phases 10 µ m porous silica 10 100 Å pores 100 pores Gary D. Christian, Analytical Chemistry, 6th ed., John Wiley & Sons, Inc., U.S.A., 2004. 2004. HPLC Stationary Phases HPLC Gary D. Christian, Analytical Chemistry, 6th ed., John Wiley & Sons, Inc., U.S.A., 2004. 2004. Normal Phase: Polar Stationary Phase, Nonpolar Mobile Phase Reversed Phase: Nonpolar Stationary Phase, Polar Mobile Phase Daniel C. Harris, Exploring Chemical Analysis, 2nd ed., W.H. Freeman and Company, New York, 2001. Freeman Effect of Solvent (k) (Reverse Phase HPLC) (Reverse A: aqueous phosphate buffer pH 3.5, B: acetonitrile; Stat. phase: 5 µ m silica modified with A: silica C18 O OH OH O HO O O O O O O O 1 2 3 4 5 6 7 8 High-Performance Liquid Chromatography (HPLC) (HPLC) Gary D. Christian, Analytical Chemistry, 6th ed., John Wiley & Sons, Inc., U.S.A., 2004. ed., Daniel C. Harris, Exploring Chemical Analysis, Daniel 3rd ed., W.H. Freeman and Company, New York, 2005. York, Solvent Gradients (Reverse Phase HPLC) (Reverse O OH OH O HO O O O O O O O 1 2 3 4 5 6 7 8 Daniel C. Harris, Exploring Chemical Analysis, 3rd ed., W.H. Freeman and Company, New York, 2005. (Reverse Phase HPLC; unstated percentages are water) Effect of Solvent (α) Effect Gary D. Christian, Analytical Chemistry, 6th ed., John Wiley & Sons, Inc., U.S.A., 2004. 2004. HPLC Absorbance Detector HPLC Daniel C. Harris, Exploring Chemical Analysis, 3rd ed., W.H. Freeman and Company, New York, 2005. Freeman Light Detector (Transducer) Light Photodiode Daniel C. Harris, Exploring Chemical Analysis, 3rd ed., W.H. Freeman and Company, New York, 2005. Freeman Diode Array Detector Diode Liquid Chromatography: Detectors Liquid • • • • UV-vis (single wavelength or diode array) UV-vis Fluorescence detector Fluorescence Refractive index detector Refractive Electrochemical detector Electrochemical ⇒ Selective detectors are useful in dedicated analysis systems when sample contain many compounds. systems ⇒ Detectors with low selectivity are useful for routine laboratories that use the same chromatograph for many different types of samples. * Order the above detectors in order of increasing selectivity. selectivity. ...
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This note was uploaded on 04/06/2011 for the course CHEM 2011 taught by Professor Buhlman during the Spring '10 term at Minnesota.

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