Lec06.Chem Separation
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Transcript of 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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FRACTIONAL DISTILLATION
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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FRACTIONAL DISTILLATION
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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AZEOTROPIC & EXTRACTIVE
DISTILLATIONS
From: Meloan, 1999. Chemical
Separations: Principles, Techniques, and
Experiments, John Wiley & Sons, Inc.,
New York.
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AZEOTROPIC & EXTRACTIVE
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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ELECTRICAL FIELD SEPARATIONS
Electrophoresis Charged molecules in solution are separated based on
differences in size and charge when a high voltage is
applied
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ELECTRICAL FIELD SEPARATIONS
+- +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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ELECTRICAL FIELD SEPARATIONS
+- +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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ELECTRICAL FIELD SEPARATIONS
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