lec06.chem separation

7/28/2019 Lec06.Chem Separation

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CHEMISTRYOF SEPARATION


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OUTLINE

Introduction

Types

Extraction

Phase changes Electric Fields

Flotation

Membranes

Other

Chromatographic


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ANALYTICAL PROCESS

Processing

Interpretation

Instrumentation

Calibration Measurement

Food

Sample

Sampling

Pretreatment

Extraction

Separation

Clean up

Concentration

Derivatization


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HOMEWORK

Using the flow diagram for the analytical process, fityour research project into an analytical process.

Food, biological tissue or fluid

Sampling

Extraction what is the analyte? Instrumentation what will you use to measure the

analyte? How will you calibrate?

Processing and interpretation


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INTRODUCTION

Separation Anderson, 1987 physical transfer of a particular

chemical substance from one phase or mediumto another, or the actual physical separation of

the components of a mixture into separatefractions.

Meloan, 1999 is a process whereby compoundsof interest are removed from the othercompounds in the sample that may reactsimilarly and interfere with a quantitativedetermination.

Seader and Henley, 1998 The separation ofchemical mixtures into their constituents.Separations including enrichment, concentration,purification, refining, and isolation.


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INTRODUCTION

Separation

Extraction

Analysis


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PHASE

Volatilization Conversion of all or part

of a solid or liquid into agas

What are ways thatsupport this conversion?Heat

Strong acids

Oxidation

Reduction

What analyticalinstrument uses thissame principle?

Gas

Chromtography


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PHASE

Distillation

The production of a vapor from liquid by heating,condensing the vapor, and collecting in a separatevessel Vapor pressure the pressure exerted by molecules that have

escaped the liquids surface

Molecules in the gas state are in constant motion

Usually several hundred miles per hour

Size, shape, and chemical properties

This relates to surface tension

Examples: simple, fractional


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FRACTIONAL DISTILLATION

Toluene + Benzene


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Plates Theoretical plates

Represent eachequilibrium step in the

refluxing system HETP (Height

Equivalent to aTheoretical Plate)Takes into account the

distance from surface ofliquid to the top of thecolumn

Measures the efficiencyof distillation


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Continuous Refluxing

Total

Partial


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HOMEWORK

Ethyl isobutyrate (b.p. = 111C) and ethyl isovalerate

(b.p. = 135C) are used for flavors and essences.

Briefly explain how fractional distillation works?

Can these be separated using this technique?

Explain you answer?

Think about theoretical plates?


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AZEOTROPIC & EXTRACTIVE

DISTILLATIONS

Azeotrope Liquid mixture

characterized by amaximum or minimum

boiling pt. (bp) which islower or higher than bpfor any of thecomponents and thatdistills without change

in composition Distillation form an

azeotrope


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DISTILLATIONS

From: Meloan, 1999. Chemical

Separations: Principles, Techniques, and

Experiments, John Wiley & Sons, Inc.,

New York.


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DISTILLATIONS

Extractive

A third component is added to extract one of the major

components

Other interactions

Hydrogen, dipole-dipole, ion-dipole, pi bonds

Solvent


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STEAM & VACUUM

DISTILLATIONS

Used for components that decompose at or near

its bp

Steam

Limited to those components that are immiscible withwater

Problem Emulsion form

Usually forms when densities of 2 liquids are similar

Breaking emulsions

Glass wool

Centrifuge

Salts

Acids

Phase separation paper (Whatman PS-1)


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STEAM & VACUUM

DISTILLATIONS

Vacuum

Any distillation below

atmospheric pressure

Advantage boiling ptdifferences increase at

reduced pressures


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SUBLIMATION

Process which

converts a solid to a

gas bypassing the

liquid phaseA solid will sublime if

its vapor pressure

reaches atmospheric

pressure below itsmelting point


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SUBLIMATION

Lyophilization


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ELECTRICAL FIELD SEPARATIONS

Gel Matrix

Electrophoresis

Disc

Isoelectric Focusing

Immuno

Capillary Electrophoresis


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Electrophoresis Charged molecules in solution are separated based on

differences in size and charge when a high voltage is

applied


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+- +F

F=QEQ, charge on the particle

E, field strength

Fs=6prhur, radius of the particle (cm), h,

viscosity of the medium

(poises), u, electrophoretic

velocity (cm/sec)

Fs

ElectrophoresisTheory

Mobility (U) requires a net electrostatic charge

Can neutral particles be separated

electrophoretically?Charging processes: acids and bases, dissociation

into ions by polar solvents, hydrogen bonding,chemical reactions, polarization, ion pair formation


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+- +F

F=QEQ, charge on the particleE, field strength

Fs=6prhur, radius of the particle (cm), h,viscosity of the medium

(poises), u, electrophoretic

velocity (cm/sec)

Fs

Thus, Fs=QE=6prhu and

U=Q/6prh

ElectrophoresisTheory


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Electrophoresis

Major problem

Heating

An increased rate of diffusion of sample and buffer ions

leading to broadening of the separated samples.

The formation of convection currents, which leads to mixing of

separated samples.

Thermal instability of samples that are rather sensitive to heat.

This may include denaturation of proteins or loss of activity of

enzymes. A decrease of buffer viscosity, and hence a reduction in the

resistance of the medium.

R = V / IR, resistance, V, voltage, I, current

W = I2RW, watts,R, resistance, I, current Smiling

http://www.mnstate.edu/marasing/CHEM480/Handouts/Chapters/Capillary%20Electrophoresis.pdf
http://www.mnstate.edu/marasing/CHEM480/Handouts/Chapters/Capillary%20Electrophoresis.pdfhttp://www.mnstate.edu/marasing/CHEM480/Handouts/Chapters/Capillary%20Electrophoresis.pdf


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FLOTATION

Purge and Trap

Foam fractionation

Gas-solid flotation

Liquid-solid flotation


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FLOTATION

Foam fractionation

Based on transferring

one or more

components in a liquid

to the surface of gas

bubbles passing

through it and

collecting the

separated componentsin a foam at the top of

the liquid.


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FLOTATION

Foam fractionation Factors

Foamers use material ofopposite charge to the sample tomake a good foam

Defoamers benzene,quanternary amines, silicones

Chain Length chain length ofnonpolar end of surfactantincreases, its absorption andseparation increases

Surfactant concentrationseparation increases asconcentration increases up to apoint

pH alters ionic species


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FLOTATION

Foam fractionationPurge and Trap

Removal and collection of

volatile compounds from a

liquid by diffusion of thevolatiles into a stream of gas

bubbles passing through it and

trapping the expelled particles.

Purpose - concentration


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FLOTATION

Foam fractionation

Purge and Trap

Purging

system

TrappingSystem


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FLOTATION

Foam fractionation Purge and Trap

Purge Efficiency

Vapor pressure higher vapor pressure, higher purgeefficiency

Solubility greater solubility in the sample matrix,harder to remove

Temperature increase in temperature alwaysincreases purge efficiency

Sample size increase sample size requires increasein purge volume

Purge volume increase in purge volume improvesefficiency

Purge method given same purge volume, fine bubbledispersion better than large bubbles


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FLOTATION

Foam fractionation

Purge and Trap

Traps

Factors for a good trap1. Retain analytes of interest

2. Allow gases to pass readily

3. Release analyte easily

4. Stabilitydont release volatiles or cause sidereactions

5. Reasonably priced


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HOMEWORK

Explain the technique of purge and trap?

Include in your explanation

What is meant by purging and trapping?

What factors influence purge efficiency?

What factors influence trap efficiency?


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MEMBRANES

Filtering and Sieving

Selectively remove a portion of a mixture by passing through a

semi-porous material

Material if porous with small pore holes filtering

Material is a screen with large pore holes screening There is a slew of filtering papers for the analytical chemist to

use

Filters with phases bonded which allows the filter to behave like a

column in HPLC or GLC


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MEMBRANES

Filtering and

Sieving


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MEMBRANES

Filtering and Sieving Proper filtering

1. Use proper grade filter; 2. Decant; 3. Use long stem funnel; 4. Use narrowdiameter stem rather than long one; 5. Use fluted funnel if possible; 6.Fold paper with 1/8 to 1/4th inch offset; 7. Tear paper at top of fold toprevent air intake; 8. Keep stem full of solution; 9. Touch end of stem toside of beaker


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MEMBRANES

Osmosis & Reverse Osmosis 2nd Law of Thermodynamics systems tend toward disorder

High concentration goes to low concentration

Osmosis involves solvent Dialysis involves solute


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MEMBRANES

Osmosis & ReverseOsmosis

Difference inthermodynamicpotential Gibbs Free

energy Higher in pure solvent

than solution

Tendency for system toreach equilibrium freeenergy equal the

difference is the drivingforce and thereforeosmosis.


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MEMBRANES

Osmosis & Reverse Osmosis Application of pressure to force the solvent back to the other side Reverse

osmosis

Parameters Diffusion coefficient D; permeability coefficient P; solubility constant S;

filtration coefficient Lp; solute permeability coefficient ; reflection coefficient


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MEMBRANES

Dialysis Removal of low molecular weight solute molecules from a

solution by passing through a semi-permeable membrane

driven by a concentration gradient

Ultrafiltration

Combination of

reverse

osmosis and

dialysis?


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OTHER TECHNIQUES

Density

Use density gradients Principle object placed

in a fluid will sink ifdensity is greater thanthe fluid, will float ifdensity less than fluid orwill stay suspended ifdensities of object andfluid are the same.

Centrifugation Separates based on density

and amplified by applying arotational force

RCF = 1.118 x 10-5 r N2where r, radial distance ofa particle from axis ofrotation in cm; N, speedof rotation in rpm


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HOMEWORK

Why is it not appropriate when describing

centrifugation protocols to list the conditions of

centrifugation in rpms?


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SOLUBILITY

Extraction Solvent

Chromatography

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