Chem. 230

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Chem. 230 9/2 Lecture
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Introduction- Instructor Roy Dixon

• Educational Background in Environmental
  Analytical Chemistry
• Most of my research currently has been in HPLC
  technology/methodology development and
  applications
• Currently, Im working on GC analysis of
  alternative fuels
• I expect to improve my knowledge of several parts
  of chromatography through teaching this class

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Introduction- Students

• Introduce yourself (name/degree plan)
• Is there anything specific you expect to get out
  of the class?

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Syllabus Top Part

• I would like to have a break mid-way through
  class (10 or 15 minutes)
• Best way for contact is by email
• Can arrange other times to meet with students
• Course information will be posted on website

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Syllabus Text Other Reading

• Text covers instrumental chromatography fairly
  well (particularly good with HPLC separations)
• Many of the pages assigned will only need to be
  skimmed over (e.g. p. 1-30)
• In other areas, additional readings will be
  assigned (either in folder or posted on website)

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Syllabus- Course Topics

• Core Topics
• Simple Extractions
• Chromatography (emphasizing instrument based
  methods)
• Mass Spectrometry (focus on use as
  chromatographic detector)
• Electrophoresis (emphasizing capillary
  electrophoresis and related topics)
• Selected Specialized Topics
• Student Presentations and Discussions
• I will give some example special topics
• GC x GC
• Aerosol-Based Detectors for HPLC

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Syllabus- Notes on Grading

• 40 Minute Exams
• Previously had 5 quizzes, but switching this
  semester due to only 14 meetings
• Used to fit with breakdown of topics and because
  of 1 long lecture
• Final Exam
• Fairly standard exam
• About 35 will come from student presentations

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Syllabus- Notes on Grading (2)

• Specialized Topic Presentation
• - Will go over handout later
• - Grading based on materials and presentation
• Application Paper
• Will research an improved method for a specific
  application (one to several related papers on a
  topic)
• Homework
• No text problems so will give practice and
  assignment problems

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Typical Lecture Style

• Announcements given in first few minutes
• Use board or document camera for working out
  example problems (a significant part to the
  course)
• Powerpoint and Handouts will be more common on
  topics not covered in detail in text
• Powerpoint slides will be made available on
  website

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Specialized Topic Presentations I

• Goal is for students to learn about new or
  emerging separation technology
• Students will be responsible for
• researching topics
• making reading material available (little or no
  photocopying,hopefully)
• understanding concepts
• preparing homework problems or questions
• preparing presentations

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Specialized Topic Presentations II

• Teams of Two
• I will give several example presentation (first
  by guest lecturer)
• See list of topics on handout, but you may want
  to modify topic or select your own topic
• If changing topic, be sure to clear it with me
• Most of the points will be for the presentation
  (grading key used previously is provided on last
  page), but there will also be points for
  preparation of reading materials and homework
  questions
• Section V show the main points needed for the
  presentation

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Applications Paper I

• Goal is for students to research an application
  of a separation method for a specific application
• The paper should focus on new developments to
  improve the separation (e.g. for either better
  isolation or for better analysis)
• Students can select application area
• Some example applications
• analysis of chiral compounds from a specific
  reaction or class of reactions to determine
• analysis of smoke tracers in atmospheric aerosols
• analysis of domoic acid in marine mammals

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Applications Paper II

• Improvements can be from one paper (should be a
  significant improvement) or a set of related
  papers
• You will also need to research past
  separation/alternative analysis methods used for
  the problem
• Details on the report are given in the handout
• Some specific requirements will be asked of you
  (e.g. estimate the cost of the equipment to
  perform the method).

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Homework Set 1

• To do before 1st Quiz.
• Longer problems are to be turned in Sept. 16.
• May add more problems to do for your benefit.
• Problems to be turned in should be worked on
  independently.

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Separation Purposes

• Isolation/Purification/Removal of Compound(s)
• Qualitative Analysis
• Quantitative Analysis

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Separations Diagram
All Separations
Non-Partitioning
Simple separations
Based on Partitioning
Filtering
Liquid-liquid extraction
Higher Resolution/Instrument Based
Capillary Zone Electrophoresis
Gas Chromatography
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Simple Separations/Extractions- Introduction

• Assigned text reading
• p. 1-26 light, background reading
• p. 27-30 covered in more detail later
• Chapter 14 covers extraction other simple
  separation methods (will cover text in more
  detail will add to this in lecture)

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Simple Separations - Purposes

• Main purpose is to remove analyte(s) from
  interferants
• A common purpose is to concentrate analyte(s)
• For complicated samples with numerous analytes,
  simple separation can be used as coarse
  separation step
• Often integrated with sample collection (e.g.
  filtration of air to collect aerosol particles)
  or sample modification (derivatization)
• Typically insufficient for isolating analytes but
  needed for reduction of interferants
• common main strategies
• isolation/trapping of analytes (usually 2 step)
• removal of contaminants (often single step)
• Primary and secondary separations

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Simple Separations- Examples of Strategies

1. You want to measure combustion exhaust gases by
   GC. There are around 15 gases of interest that
   are present at moderately high concentrations.
   Water also is present at high concentration and
   interferes.
2. You are interested in measuring phenols present
   in sea-water at very low concentrations by HPLC.
   Interference by other organics is not a major
   issue.
3. You are interested in analyzing oligosaccharides
   present in glycoproteins by HPLC. There are
   close to 100 compounds of interest present in the
   sample.

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Simple Separations

• Almost all separations require more than one
  discrete phase
• The most common separations involve partitioning
  between two phases
• X(phase 1) ? X(phase 2)
• Some types of non-partitioning separations
  (mostly involving physical separations)
• Filtration (removal of solids from gases or
  liquids)
• Centrifugration (removal of solids from liquids)
• Membrane based separations (separation based on
  molecule size or charge)

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Simple Separations

• An effective simple separation requires effective
  phase transfer plus significant differences in
  process between analyte and contaminants (good
  selectivity)
• Sample preparation steps often require as much or
  more analyst time as instrument based analysis
  (i.e. are labor-intensive)
• Preferred processes are simpler, require less
  equipment, faster, effective with volumes
  desired, can be automated
• For concentrating samples, it is important that
  the method can handle large sample volumes, but
  result in small processed volumes

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Types of Simple Separations
Phases Examples
Gas - Liquid Distillation (l to g), denuders (g to l), bubblers (g to l), condensation (g to l)
Liquid - Liquid Liquid Liquid Extraction (to be covered in detail)
Gas - Solid Adsorption tubes (g to s), sublimation (s to g), freeze-drying (s to g), filtration
Liquid - Solid Dissolution (s to l), Soxhlet extraction (s to l), precipitation (l to s), filtration
Supercritical Fluid - Solid Supercritical Fluid Extraction (s to sfc)
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Gas Liquid Separations
Sample Air

• Gas Sampling
• Bubblers
• Mist Chambers (show)
• Denuders
• (above for water soluble gases)
• Cold Traps

Gases trapped on wall coating
Aerosols pass to filter
Bubbler
To filter, pump
Denuder
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Gas Liquid Separations

• Basis for Partitioning
• Into water Henrys Law
• KH X/PX where KH is the Henrys Law Constant
• KH f(T), PX partial pressure of X,
• X Molar conc. of X
• Cold Trap boiling point temperature

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Gas Liquid Separations

• Headspace Analysis (GC method)
• Sample in vial with liquid and gas phases
• Headspace gas withdrawn with syringe for
  injection into GC (or other device)

septum
Headspace
liquid
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Gas Liquid Separations
He to waste
He in
He in

• Purge and Trap (GC method)
• Aqueous sample or gas sampled trapped in water
• Steps 1) gas purge of water to trap, 2) heating
  of trap to GC (or other device)

Heat applied
Trapped analyte
To GC
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Gas Liquid Separations

• Distillation/Evaporation
• Evaporation used for low volatility liquid (or
  solid)
• Distillation for collection of volatile analyte
  in liquid
• Partitioning to gas phase based on Raoults Law
  (although non-ideality often occurs)
• PA XAPA where
• PA partial pressure of gas A
• XA mole fraction of A in liquid
• PA partial pressure of gas A above a pure A
  liquid
• Complete separation of two volatile components is
  often difficult

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Simple Separations Gas/Liquid
A is more volatile (lower Tb)

• Distillations
• Behavior given in T vs X plots
• 80 B example
• Vapor (condensate) is 30 B
• Multistep/stage distillation results in
  separation
• With azeotropes (non-ideal), complete separation
  is impossible (no less than 15 B in vapor)

T
Vapor
V L
Liquid
Xi
100 A
100 B
Azeotropic mixture
P
Xi
100 A
100 B
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Simple Separations Gas/Liquid

• Many other separations possible
• Unusual Separation Analysis of dissolved SO2 in
  cloud water (my dissertation project)

Counter-flow Virtual Impactor
SO2
Probe attached to airplane flying to left
Scrubbed air goes to tip and splits into 2 flows
SO2
Counter flow out of probe tip keeps gaseous SO2
out
Cloud droplets evaporate releasing SO2 which
flows to detector
Cloud droplets have inertial and make it into
probe
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Some Questions

1. If it is desired to trap a gas phase analyte in
   water, what type of values of Henrys law
   constants are desired?
2. For desorption of gases from liquids, what type
   of values of Henrys law constants are desired?
3. How can temperature adjustments be made to
   improve Henrys law constants for trapping or
   desorbing gases?
4. How can trapping of acetic acid in aqueous
   solution be improved? What about desorption?
5. How can trapping of ammonia in aqueous solution
   be improved?

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Some More Questions

1. If produced correctly, biodiesel is made up of
   fatty acid methyl esters (for fatty acids between
   12 and 20 carbons) of low/moderate volatility.
   Methanol can be a contaminant from its production
   and is much more volatile. What separation step
   could be used to separate methanol from more
   volatile constituents? Would that also work well
   if analyzing B20 (20 biodiesel/80 petroleum
   diesel?
2. Which component will be enriched in the original
   solution after distillation (based on the phase
   diagram below)?

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Still Mome Questions

• 3. Based on the phase diagram to the right, is it
  possible to isolate pure A through
  multi-step/stage distillation starting from 65
  B?
• 4. Is it possible to isolate pure B by removing A
  through multi-step/stage distillation (starting
  at same point)?

T
X
100 A
100 B
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Extractions Solid to Liquid

• Dissolution
• Dissolution Aides
• Ultrasound bath
• Other mechanical shaking
• Soxhlet Extractions (show device)
• Extraction speed is often limited by physical
  process
• Extraction from fine grain particles is easier
  than large solids

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Extractions Liquid to Solid

• Trapping applications (such as solid phase
  extraction discussed later)
• Precipitation/Filtration (or centrifugation)
• A way to separate components based on one
  component having lower solubility in a particular
  solvent or with particular counter ions
• Precipitation of ions
• Use of polar/non-polar liquids for compounds of
  variable polarity
• Phase separation by filtration or centrifugation
  most common

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Extractions Liquid to Solid

• Precipitations
• Removal of ionic compounds/highly polar
  compounds. Through addition of less polar
  organic solvent (e.g. ethanol) to water
• Removal of less polar compounds from organic
  solvent by adding more polar solvent (e.g.
  addition of ethanol to CH2Cl2 or water to ethanol)

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Extractions Liquid to Solid

• Precipitations
• Of Ions
• Can select counter ion that will selectively
  precipitate one ion but not the other ion (ion to
  be precipitated should have lower Ksp, although
  will also depend on stoichiometry)
• Can use Ksp values to calculate how successful
  the separation will be

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Extractions Liquid to Solid

• Precipitation Example
• Separation of Sr2 from Ca2
• An examination of Ksp shows smaller Ksp for SrSO4
  vs. CaSO4 (3.2 x 10-7 vs 2.4 x 10-5)
• If a mixture contains 1.0 x 10-2 M Sr2 and Ca2,
  how much SO42- can be added before Sr2 starts to
  precipitate?, before Ca2 starts to precipitate?
  What of Sr can be isolated?

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Extractions Liquid to Solid

• Temperature in precipitation processes
• Example Acetic Acid and Water

Liquid path for cooling 50 acetic acid in water
Eutectic Point
Liquid solution
T
Ice CH3CO2H (l)
CH3CO2H(s) H2O(l)
Solid solution
0
100
X(CH3CO2H)
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Some Questions From Last Lecture

1. What are advantages and disadvantages of Soxhlet
   extractions?
2. Suggest a way to isolate a polar organic compound
   from ionic compounds in urine.
3. It is desired to isolate CN- from CO32- by adding
   Ag and monitoring Ag electrochemically.
   Assuming initial concentrations of CN- 1.0 x
   10-3 M and CO32- 5.0 x 10-3 M and given Ksp
   values for AgCN and Ag2CO3 are 2.2 x 10-16 and
   8.2 x 10-12, respectively, what would be the
   target Ag? Will this separation be very
   efficient?
4. Can acetic acid be isolated from all solutions in
   water by freezing it out?

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More Questions

• A 1.00 L sample of sea water is analyzed for
  phenols. The 1.00 L sample is passed through a
  solid phase extraction cartridge to trap the
  phenols. Then 25.0 mL of methanol is used to
  remove the phenols and then reagents are added
  that convert the phenols to methoxyphenols. The
  methoxyphenols are extracted by adding 25 mL of
  water to the methanol and extracting with two
  successive 25 mL portions of hexane. The hexane
  portions are combined, evaporated, and
  redissolved in 2.0 mL of hexane. An aliquot is
  then determined by GC and found to contain 22.1
  mmol L-1 of a particular phenol. What was the
  original conc. of that phenol in sea water (in
  nmol L-1) if it is assumed that all transfers
  were 100 efficient? How could the sensitivity
  of the method be increased?
• The total NH3 (NH3 NH4) concentration of a
  water sample is determined by NH3 in the
  headspace above a sample. A water sample at a pH
  of 8.1 was found to have a headspace pressure of
  2.4 x 10-7 atm. If KH 1.6 x 10-5 atm m3/mol
  (at that T) and Ka(NH4) 5.6 x 10-10.,
  calculate the total NH3 concentration in the
  sample

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Liquid-Liquid Extractions

• One of more common simple separations
• Often used to introduce partition theory
• Equipment is simple (separation funnel or vials
  syringes)
• Two liquids must be immiscible (form two distinct
  phases)
• Lower phase is more dense (usually water or
  chlorinated hydrocarbon)
• Most common with water (or aqueous buffer) and
  less polar organic liquids

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Liquid-Liquid Extractions

• Partition Coefficient
• Kp Xraffinate/Xextractant
• Kp depends on thermodynamics of dissolving X in
  two phases
• Most common rule for solubility is likes dissolve
  likes
• More polar compounds exist in greater
  concentration in water
• Koctanol-water values can be found in reference
  tables (octanol is assumed to be the raffinate)

X(org)
X(aq)
If sample starts in aq phase, aq phase is
raffinate, org is extractant
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Next Time

• Will cover liquid liquid extractions from a
  quantitative perspective in more detail