221-chapter-23

221-chapter-23 - Introduction to Analytical Separations...

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Introduction to Analytical Separations Introduction 1.) Sample Purity Many chemical analysis are not specific for one compound - Actually respond to many potential interferences in the sample Often it is necessary to first purify the compound of interest - Remove interfering substances before a selective analysis is possible - This requires a separation step. 2.) Techniques available for Chemical Separations: Extraction Distillation Precipitation Chromatography Many others (centrifugation, filtration, etc) Extractions and Chromatography are especially useful in analytical methods
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Electrophoresis (1997) 18:1259-1313 Introduction to Analytical Separations 2D Gel Electrophoresis of total protein extract from E. coli cells Toxicological Sciences (2000) 57:326-337 NMR Spectra of Mouse Urine after treatment with a Drug Introduction 3.) Illustration Biological Samples are Composed of Complex Mixtures - Analysis of composition and changes help in understanding disease and the development of treatments Analysis of Various Pesticides in Ground water using LC-MS Journal of Chromatography A, 1109 (2006) 222–227
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Extractions 1.) Definition The transfer of a compound from one chemical phase to another - The two phases used can be liquid-liquid, liquid-solid, gas-solid, etc - Liquid-liquid is the most common type of extraction - The partitioning of solute s between two chemical phases (1 and 2) is described by the equilibrium constant K Introduction to Analytical Separations 1 2 ] S [ ] S [ K = K is called the partition coefficient Immiscible liquids
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Introduction to Analytical Separations Extractions 2.) Extraction Efficiency The fraction of moles of S remaining in phase 1 after one extraction can be determined - The value of K and the volumes of phases 1 and 2 need to be known The fraction of S remaining in phase 1 after n extractions is ( 29 2 1 1 KV V V q + = where: q = fraction of moles of S remaining in phase 1 V 1 = volume of phase 1 V 2 = volume of phase 2 K = partition coefficient ( 29 n n KV V V q + = 2 1 1 Assumes V is constant
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Introduction to Analytical Separations Extractions 2.) Extraction Efficiency Illustration Ether layer Water layer 1M UO 2 (NO 3 ) 2 (yellow) After mixing, UO 2 (NO 3 ) 2 Is distributed in both layers After 8 extractions, UO 2 (NO 3 ) 2 has been removed from water
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Introduction to Analytical Separations Extractions 3.) What happens as n approaches infinity? Eventually the amount of S remaining in phase 1 becomes zero - Solution is infinitely diluted This Situation Created a Strange Saga in Science – Water Memory - a founding principal of homeopathic medicine - the claim is that water remembers the activity of the drug after it has been removed Nature (1988) 333:816-818 Authors’ claim to still observe antibody activity even after a 1x10 120 fold dilution. Less than 1
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This note was uploaded on 05/09/2010 for the course CHEM 221 taught by Professor Dr.robertpowers during the Fall '07 term at San Diego.

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221-chapter-23 - Introduction to Analytical Separations...

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