Chem. 231 – 2/4 Lecture
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)
• I’m Working on Procedures for Set 2 Labs
Announcements II
• Today’s 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
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
– Today’s work should be focused on learning
to use instruments
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
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
Simple Extractions
Gases 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)
Simple Extractions
Gases to Solids
• Traditional method to trap gases (e.g.
volatile hydrocarbons) using cartridge
heating wire
trapping
flow
– 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
Simple Extractions
Gases 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)
Simple Extractions
Filtration/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)
Simple Extractions
Liquid – 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)
Simple Extractions
Liquid – 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
Simple Extractions
Solvent 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
to vacuum bleed
(control), traps
and vacuum
pump
condensor
rotation
– Typically used with solvents more volatile than
water
– Has both pressure and temperature controls
(usually manual)
round bottom
– Bumping can occur
flask
water bath
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)
Some Questions
1.
2.
3.
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.
Small quantities of particulates are expected in mL
samples to be analyzed by HPLC. Suggest a way to
remove them.
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?
Simple Extraction
Gas 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
For lab work, it is critical to have the sheath
on when piercing septum
Fiber
GC Inlet