Chem. 231

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Chem. 231 2/4 Lecture
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Announcements I

• Homework Set 1 is due 2/6
• New Set will be available 2/6 (hopefully) which
  will be due 2 weeks later
• Quiz 1 on 2/11 on homework and topics covered in
  class (setting up files, data transfer and
  processing, and simple extraction covered today)
• Website Update
• Writing guidelines
• List of Books and Journals
• Example Quiz (from 2007)
• Im Working on Procedures for Set 2 Labs

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Announcements II

• Todays Topics
• Simple Extractions (emphasis on equipment,
  procedures and tests and on ones we can do)
• Solids into liquids
• Gases into liquids
• Gases into solids
• Solids from liquids or gases (filtration)
• Liquids into liquids
• Solvent removal

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Announcements III

• Lab Today
• Set 1 Labs are ready (but work was not planned in
  syllabus)
• Should plan on making a multi-component standard
  for qualitative analysis
• Todays work should be focused on learning to use
  instruments

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Simple Extractions

• Purposes (repeat from Chem 230)
• Isolate compound of interest (only very simple
  samples)
• Trap and Concentrate Analyte(s)
• Remove interferences
• Split sample into classes

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Simple Extractions

• Solid into Liquid
• Best to choose solvent with good solubility for
  analytes (e.g. similar Kow and functional groups
  as solvent)
• Sample prep (finely ground powder will lead to
  better extraction)
• Agitation (shakers, ultrasound bath)
• Soxhlet Extractors

Soxhlet Extractor show example
to condensor
Extraction Thimble
round bottom flask with solvent
1) Round bottom flask is heated, solvent
evaporates
2) Solvent condenses and fills extraction thimble
3) Once reaching loop, solvent siphons out and
back to round bottom flask
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Simple ExtractionsGases to Liquids

• May be used for trapping carbonyls in
  derivatization lab
• Equipment (repeat from Chem 230)
• Bubblers, mist chambers, denuders
• Best Conditions (larger KH constants)
• lower temperatures
• solvent polarity (although less volatile solvents
  needed)
• pH (if trapping acids or bases)

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Simple ExtractionsGases to Solids
heating wire
trapping flow

• Traditional method to trap gases (e.g. volatile
  hydrocarbons) using cartridge
• Can be combined with purging to transfer volatile
  compounds from water to solid
• Desorption flow direction is usually reversed
• Most commonly used with thermal
  desorption/injection into GC
• Best Conditions
• Keep cartridge cool during trapping
• Can choose trapping material for selectivity or
  efficiency

desorbing flow
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Simple ExtractionsGases to Solids - SPME

• SPME is used most with GC analysis
• More on procedure later since can also be used
  for liquid samples and with liquid removal
• Will use in extraction lab (headspace for
  standards and samples)
• Advantages
• simple (no solvent for gases)
• efficient
• Disadvantages
• not exhaustive
• harder to make quantitative (must maintain
  similar conditions)

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Simple ExtractionsFiltration/Centrifugation

• Purpose
• to trap precipitated analytes/solutes (solids
  from liquids)
• to trap aerosol particles (from gases)
• to remove solids (needed before HPLC/GC analysis)
• Centrifugation (only for liquids)
• Best if isolating solids
• Filtration
• Large quantities (use side arm flasks)
• Small quantities (use syringe filters)

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Simple ExtractionsLiquid Liquid Extraction

• Equipment (show examples)
• traditional separatory funnel (show example)
• smaller scale conical vials (cone shape needed
  to remove most of one phase) syringes
• Separation Basis polarity partitioning
  (remember likes dissolves likes rule)
• Liquid Phases
• Two phases must be immiscible (form two distinct
  layers)
• Most common with water organic
• Also possible with polar non polar organic
  (methanol hexane), but few organic solvent sets
  are immiscible
• Lower layer is denser (water in hexane water but
  chloroform in water chloroform)

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Simple ExtractionsLiquid Liquid Extraction

• Practical Aspects
• solvent choices
• common to remove compounds from water to go to
  organic solvent (faster evaporation, better for
  GC injection)
• organic solvent (non-polar solvent for least
  polar analytes, moderately polar for somewhat
  polar analytes)
• emulsions make some liquid liquid extractions
  problematic
• selectivity also is important (e.g. use of
  toluene to selectively retain aromatics over
  alkanes)
• modifiers
• can modify water by adjusting pH (ionized
  compounds stay in water)
• salts can also be added to help in transferring
  organics to organic phase

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Simple ExtractionsSolvent Reduction/Removal

• Purposes
• Switch solvents (e.g. methanol to CDCl3 for NMR)
• Concentrate sample
• Remove volatiles
• Nitrogen drying
• used with volatile solvents/volatile solutes
• often for solvent reduction (not complete
  removal)
• Rotory Evaporators
• Typically used with solvents more volatile than
  water
• Has both pressure and temperature controls
  (usually manual)
• Bumping can occur

to vacuum bleed (control), traps and vacuum pump
condensor
rotation
round bottom flask
water bath
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Simple Extractions Solvent Reduction/Removal

• Freeze Drying
• More commonly used with water
• Better for many biological samples (susceptible
  to thermal decomposition)
• Procedure
• Sample is frozen
• Sample in container is connected to a vacuum
  (with low T water trap between sample and vacuum)
• Low pressure causes water to stay in ice form
• Difficult with small samples (can melt before
  connection is complete)

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Some Questions

1. A chemist is interested in extracting furanyl
   compounds from charred wood. Chunks of charred
   wood are placed in methanol and shaken for 30
   minutes. Repeated extractions show the
   efficiency is not great. List two ways to
   improve extraction.
2. Small quantities of particulates are expected in
   mL samples to be analyzed by HPLC. Suggest a way
   to remove them.
3. Describe how a chromatogram produced by
   Chemstation (Agilent 1100 system) can be
   transferred to an Excel file. In this method,
   will how it was integrated be retained?

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Simple ExtractionGas to Solid SPME Procedure

• Will be used in SPME lab
• The needle pierces the septum to a sample (sample
  can be gas, liquid, or headspace)
• The sheath is removed allowing trapping of
  analytes on fiber
• Stirring helps the transfer
• The sheath goes back and the needle is withdrawn
• The needle pierces the septum to a GC, the sheath
  is withdrawn and the analyte is desorbed by the
  heated GC injector

Fiber
For lab work, it is critical to have the sheath
on when piercing septum
GC Inlet