Ch25-To-PDF

Ch25-To-PDF - 1 Chapter 25 HPLC High Pressure Liquid...

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1 Chapter 25 H P LC High P ressure Liquid Chromatography c xÜyÉÜÅtÇvx P $ P riced $
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2 The Column Guard column removes dust, particles, irreversibly adsorbed impurities. Your column is a stainless-steel, 4 × 150 mm, 5- µ m silica-supported, C 18 , reversed-phase column silica-O-Si(CH 3 ) 2 -[CH 2 (CH 2 ) 16 CH 3 ] Porous frits distribute liquid evenly across the area of the column.
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3 Small particles give high efficiency but require high pressure Azo compounds run on (a) 10- µ m-diameter and (b) 5- µ m-diameter silica particles. Plate height as a function of flow rate for stationary-phase particle size of 10, 5, and 3 µ m. N ~ 3,500 L (cm) N = number of plates d p (mm) L = column length d p = particle diameter
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4
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5 The Stationary Phase Most common is spherical, microporous silica particles. Schematic of silica gel . Has up to 8 µ mol of silanol groups per square meter. SiOH p K a range is broad, centered around 5.
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6 Scanning electron micrographs of silica particles . Aggregate of spherical particles with 50% porosity and surface area of 150 m 2 /g. Spongelike structure with 70% porosity and 300 m 2 /g. Nominal pore sizes are ~10 nm, but distribution is greater in b, which also dissolves more readily in base.
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7 Example of peak “tailing , in this case of alkaloids (organic amines) in chromatogram. Less acidic silica with fewer SiOH groups is used for chromatogram.
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8 Monolithic Silica Columns (a) Single porous silica rods polymerized in (a) shape from liquid precursors. (b) ~2
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This note was uploaded on 03/28/2011 for the course CHEM 300L at USC.

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Ch25-To-PDF - 1 Chapter 25 HPLC High Pressure Liquid...

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