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Chemical Separations

303451

Somsak SirichaiLecturer

Semester 1/2002

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Lecturer: Somsak SirichaiOffice: Chemistry building, room c307Phone: 038 745900 ext.3114E-mail: sirichai@bucc4.buu.ac.th

Office Hours: Tuesday 8-10 am

Code: 303451Subject: Chemical Separations

Credits: 2(2-0-4)Lecture: Chemistry building, room c310

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Course Description: Study chemical separations. Topics: Volatilization, Distillation, Extraction, Ion Exchange, Chromatography and Electroseparation

Grading:Midterm exam 40%Final exam 40%Assignments 10%Quizzes 10%

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Text: NonePrimary References:• Karger, Snyder & Horvath; An Introduction to Separation Science• Meloan; Chemical Separations Principles, Techniques, and Experiments• Jönsson; Chromatographic Theory and Basic Principles• Ahuja; Trace and Ultratrace Analysis by HPLC• Khaledi; High Performance Capillary Electrophoresis

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What is separation?‘a process whereby the compounds of interest are removed from the other compounds in the sample that may react similarly and interfere with a quantitative determination’• important in the preparation of pure

compounds• often complex and may require several

different methods and much time before the final determinative step

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Terms common to chemical separations• cleanup

• spiking

a practical term used to describe the handling of a sample before the measuring step

the addition of a known amount of a standard to a sample so that recoveries can be determined and to calibrate the signal for quantitation

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Percent recovery:The amount of a spike that can be recovered when processed through the entire analysis procedure

values of 95-105% are desired.if <80%, modify the method.

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Separation Methods:

• phase changes• extraction

• ion exchange resins• chromatography• electric field• flotation

• membranes• miscellaneous techniques

separations involving

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Phase changes sample

no vacuum applied vacuum applied

solidto

gas or vapor

solidto

liquid

liquid to

vapor

liquid to

vapor

solid to

vapor

volatilization zonemelting

(batch, azeotropic, extractive, steam, immiscible solvents) distillation

(vacuum, molecular,sublimation) distillation

Lyophilization

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Extraction sample

liquid solid

liquidto

liquid

Liquid toliquid

countercurrent

liquid to

solid

solid to

liquid

solid to

vapor

Batch,Continuous solvent heavier,Continuous solvent lighter countercurrent

SPE Continuous(soxhlet)

Supercriticalfluid (SFE)

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Ion exchange resins

sample

Ionic molecules Ionic or polar

molecules

Neutral molecules

Ion exchangeIon chromatography

Ion retardationIon exclusion

Ligand Exchange

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Chromatography sample

Liquidmobile phase

gasmobile phase

Liquidmobile phase

column flat

gravity flow

pressure applied

• displacement• multicolumn• affinity

• size exclusion• flash• high performance

• gas-liquid

• paper• thin layer

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Electric fields sample

Ions deposited as metal

electrodeposition Gel type matrix required

yes no

electrophoresis• Capillary zone electrophoresis• Field flow fractionation

• horizontal• immunoelectrophoresis• disc• ion focusing

yesno

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Volatilization

‘the conversion of all or part of solid ora liquid to a gas’

The gas may be produced by:1. direct heating

2. applying the principle that strongacids displace weaker acids andstrong bases displace weaker bases

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Example:

• the evolution of CO2(g), weak acid, from solid CaCO3 by adding HCl,a strong acid

• the removal of NH3(g), a weak base, from solid (NH4)2SO4 by adding NaOH

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3. by oxidation• burning a sulfide in air to produce SO2

4. by reduction, or converting the elements to hydrides, such as AsH3, H2Se•

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Techniques1. Moisture determination

Fig. Microwave oven for drying food

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2. Determination of Mercury in the Environment by Volatilization

Fig. Apparatus for flameless AAS

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Next lecture:

Distillation