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Instrumental Lecture 12

Instrumental Lecture 12 - Chapter 26 An Introduction to...

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Chapter 26: An Introduction to Chromatographic Separations Column Chromatography Migration Rates – Distribution Contstants – Retention Times – Selectivity Factor Zone Broadening & Column Efficiency Optimizing Performance • Resolution
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Partitioning = type of equilibrium where the analyte divides itself between two phases For liquid-liquid extraction – two liquids For chromatography – mobile vs. stationary phases Define a partition ratio K (or distribution constant ) C s where C s & C M are K = ------- C M concentrations of analyte in stationary & mobile phases
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A & B retained by column differently B has higher K B takes longer to elute from column Detector sees A first then B Peak heights & peak areas are proportional to conc. Band broadening
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t M = time for unretained molecule to reach detector or dead time t R = retention time, time for retained species to reach detector
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