Quant_Lect_14_LC - Liquid Chromatography Page 1 of 2 Liquid...

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Liquid Chromatography I. Mobile phases and programmed elution A. Stationary phase must reversibly bind analytes; solvent must dissolve analytes B. Adjust k by varying mobile phase composition, increasing polarity with time C. Common mobile phases are hexane, dioxane, methanol, acetonitrile, water D. Buffers critical to correct separation. How to make an accurate buffer in a non- aqueous solvent. II. Columns A. particle size typically 3 microns or less. Diffusion time/distance relationship is d = (2Dt) 1/2 , D ~ 10 -6 cm 2 s -1 , so t ~ 45 ms to diffuse across particle, sub-ms to go from center of flow to particle surface. B. pressure, flow rate. Viscosity results in back-pressure. 0.1 ml min -1 with 10 cm long column may require 1000 psi. Void volume ~ 0.1 mL gives void time ~ 1 minute, total elution time 10-20 min for useful separation (k<20). Ultrahigh performance LC uses particles < 1 μm in diameter, pressure > 50000 psi = 3000 atmospheres. C. Typical normal phase: amino-, hydroxy-, or cyano-alkyl bonded to siloxane.
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This note was uploaded on 04/02/2012 for the course CHEMISTRY 222 taught by Professor Mcdonald during the Fall '11 term at University of Illinois, Urbana Champaign.

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Quant_Lect_14_LC - Liquid Chromatography Page 1 of 2 Liquid...

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