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Chemistry of Separation. Outline. Introduction Types Extraction Phase changes Electric Fields Flotation Membranes Other Chromatographic. Sampling. Instrumentation. Processing. Sample. Calibration. Measurement. Interpretation. Pretreatment. Extraction. Separation. Clean up.

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outline
Outline
  • Introduction
  • Types
    • Extraction
    • Phase changes
    • Electric Fields
    • Flotation
    • Membranes
    • Other
    • Chromatographic
analytical process

Sampling

Instrumentation

Processing

Sample

Calibration

Measurement

Interpretation

Pretreatment

Extraction

Separation

Clean up

Concentration

Derivatization

Analytical Process

Food

homework
Homework
  • Using the flow diagram for the analytical process, fit your 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
introduction
Introduction
  • Separation
    • Anderson, 1987 “physical transfer of a particular chemical substance from one phase or medium to another, or the actual physical separation of the components of a mixture into separate fractions.”
    • Meloan, 1999 “is a process whereby compounds of interest are removed from the other compounds in the sample that may react similarly and interfere with a quantitative determination.”
    • Seader and Henley, 1998 “The separation of chemical mixtures into their constituents. Separations including enrichment, concentration, purification, refining, and isolation.”
phase

Gas Chromtography

Phase
  • Volatilization
    • Conversion of all or part of a solid or liquid into a gas
    • What are ways that support this conversion?
      • Heat
      • Strong acids
      • Oxidation
      • Reduction
    • What analytical instrument uses this same principle?
phase8
Phase
  • Distillation
    • The production of a vapor from liquid by heating, condensing the vapor, and collecting in a separate vessel
      • Vapor pressure – the pressure exerted by molecules that have escaped the liquid’s 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
fractional distillation
Fractional Distillation

Toluene + Benzene

fractional distillation10
Fractional Distillation
  • Plates
    • Theoretical plates
      • Represent each equilibrium step in the refluxing system
    • HETP (Height Equivalent to a Theoretical Plate)
      • Takes into account the distance from surface of liquid to the top of the column
      • Measures the efficiency of distillation
fractional distillation11
Fractional Distillation
  • Continuous Refluxing
    • Total
    • Partial
homework12
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?
azeotropic extractive distillations
Azeotropic & Extractive Distillations
  • Azeotrope
    • Liquid mixture characterized by a maximum or minimum boiling pt. (bp) which is lower or higher than bp for any of the components and that distills without change in composition
    • Distillation – form an azeotrope
azeotropic extractive distillations14
Azeotropic & Extractive Distillations

From: Meloan, 1999. Chemical Separations: Principles, Techniques, and Experiments, John Wiley & Sons, Inc., New York.

azeotropic extractive distillations15
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

steam vacuum distillations
Steam & VacuumDistillations
  • Used for components that decompose at or near its bp
  • Steam
    • Limited to those components that are immiscible with water
      • 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)
steam vacuum distillations17
Steam & VacuumDistillations
  • Vacuum
    • Any distillation below atmospheric pressure
    • Advantage boiling pt differences increase at reduced pressures
sublimation
Sublimation
  • Process which converts a solid to a gas bypassing the liquid phase
  • A solid will sublime if its vapor pressure reaches atmospheric pressure below its melting point
sublimation19
Sublimation
  • Lyophilization
electrical field separations
Electrical Field Separations
  • Gel Matrix
    • Electrophoresis
      • Disc
      • Isoelectric Focusing
      • Immuno
  • Capillary Electrophoresis
electrical field separations21
Electrical Field Separations
  • Electrophoresis
    • Charged molecules in solution are separated based on differences in size and charge when a high voltage is applied
electrical field separations22
Electrical Field Separations
  • Electrophoresis
    • Theory
      • 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

Fs

F

-

+

+

Fs=6prhu

r, radius of the particle (cm), h, viscosity of the medium (poises), u, electrophoretic velocity (cm/sec)

F=QE

Q, charge on the particle

E, field strength

electrical field separations23
Electrical Field Separations
  • Electrophoresis
    • Theory

Fs

F

-

+

+

Fs=6prhu

r, radius of the particle (cm), h, viscosity of the medium (poises), u, electrophoretic velocity (cm/sec)

F=QE

Q, charge on the particle

E, field strength

Thus, Fs=QE=6prhu and

U=Q/6prh

electrical field separations24

Smiling

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 / I

R, resistance, V, voltage, I, current

W = I2 R

W, watts,R, resistance, I, current

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

flotation
Flotation
  • Purge and Trap
  • Foam fractionation
    • Gas-solid flotation
    • Liquid-solid flotation
flotation26
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 components in a foam at the top of the liquid.
flotation27
Flotation
  • Foam fractionation
    • Factors
      • Foamers – use material of opposite charge to the sample to make a good foam
      • Defoamers – benzene, quanternary amines, silicones
      • Chain Length – chain length of nonpolar end of surfactant increases, its absorption and separation increases
      • Surfactant concentration – separation increases as concentration increases up to a point
      • pH – alters ionic species
flotation28
Flotation
  • Foam fractionation
      • Purge and Trap
        • Removal and collection of volatile compounds from a liquid by diffusion of the volatiles into a stream of gas bubbles passing through it and trapping the expelled particles.
        • Purpose - concentration
flotation29
Flotation
  • Foam fractionation
      • Purge and Trap

Trapping

System

Purging system

flotation30
Flotation
  • Foam fractionation
      • Purge and Trap
        • Purge Efficiency
          • Vapor pressure – higher vapor pressure, higher purge efficiency
          • Solubility – greater solubility in the sample matrix, harder to remove
          • Temperature – increase in temperature always increases purge efficiency
          • Sample size – increase sample size requires increase in purge volume
          • Purge volume – increase in purge volume improves efficiency
          • Purge method – given same purge volume, fine bubble dispersion better than large bubbles
flotation31
Flotation
  • Foam fractionation
      • Purge and Trap
        • Traps
          • Factors for a good trap
          • Retain analytes of interest
          • Allow gases to pass readily
          • Release analyte easily
          • Stability – don’t release volatiles or cause side reactions
          • Reasonably priced
homework32
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?
membranes
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
membranes34
Membranes
  • Filtering and Sieving
membranes35
Membranes
  • Filtering and Sieving
    • Proper filtering

1. Use proper grade filter; 2. Decant; 3. Use long stem funnel; 4. Use narrow diameter 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 to prevent air intake; 8. Keep stem full of solution; 9. Touch end of stem to side of beaker

membranes36
Membranes
  • Osmosis & Reverse Osmosis
    • 2nd Law of Thermodynamics – systems tend toward disorder
    • High concentration goes to low concentration
    • Osmosis involves solvent
    • Dialysis involves solute
membranes37
Membranes
  • Osmosis & Reverse Osmosis
    • Difference in thermodynamic potential – Gibbs Free energy
      • Higher in pure solvent than solution
      • Tendency for system to reach equilibrium – free energy equal – the difference is the driving force and therefore osmosis.
membranes38
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 
membranes39
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?
other techniques
Other Techniques
  • Density
    • Use density gradients
      • Principle – object placed in a fluid will sink if density is greater than the fluid, will float if density less than fluid or will stay suspended if densities of object and fluid are the same.
  • Centrifugation
    • Separates based on density and amplified by applying a rotational force
      • RCF = 1.118 x 10-5 r N2 where r, radial distance of a particle from axis of rotation in cm; N, speed of rotation in rpm
homework41
Homework
  • Why is it not appropriate when describing centrifugation protocols to list the conditions of centrifugation in rpm’s?
solubility
Solubility
  • Extraction
    • Solvent
  • Chromatography