Chem. 230 – 9/2 Lecture
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, I’m working on GC analysis of
alternative fuels
• I expect to improve my knowledge of several
parts of chromatography through teaching
this class
Introduction
- Students
• Introduce yourself (name/degree plan)
• Is there anything specific you expect to
get out of the class?
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
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)
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
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
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
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
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
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
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
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).
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.
Separation Purposes
• Isolation/Purification/Removal of
Compound(s)
• Qualitative Analysis
• Quantitative Analysis
Separations Diagram
All Separations
Simple
Based on Partitioning
separations
Liquid-liquid extraction
Non-Partitioning
Filtering
Higher Resolution/Instrument Based
Gas Chromatography
Capillary Zone
Electrophoresis
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)
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
Simple Separations
- Examples of Strategies
1.
2.
3.
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.
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.
You are interested in analyzing oligosaccharides
present in glycoproteins by HPLC. There are close to
100 compounds of interest present in the sample.
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)
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 laborintensive)
• 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
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)
Gas – Liquid Separations
Sample Air
• Gas Sampling
– Bubblers
– Mist Chambers
(show)
– Denuders
(above for water
soluble gases)
Gases
trapped on
wall coating
Bubbler
Aerosols pass
to filter
To filter,
pump
– Cold Traps
Denuder
Gas – Liquid Separations
• Basis for Partitioning
– Into water: Henry’s Law
KH = [X]/PX
where KH is the Henry’s Law Constant
KH = f(T), PX = partial pressure of X,
[X] = Molar conc. of X
– Cold Trap: boiling point temperature
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
Gas – Liquid Separations
• 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)
He in
He in
He to
waste
Heat
applied
Trapped
analyte
To GC
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 Raoult’s 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
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 (nonideal), complete
separation is
impossible (no less
than 15% B in vapor)
T
Vapor
V+L
Liquid
100% A
Xi
100% B
Azeotropic mixture
P
100% A
Xi
100% B
Simple Separations – Gas/Liquid
• Many other
separations possible
• Unusual Separation:
SO
Analysis of dissolved
SO2 in cloud water
(my dissertation
project)
Counter-flow Virtual Impactor
2
Scrubbed air goes to tip and
splits into 2 flows
Counter flow out of probe tip
keeps gaseous SO2 out
Cloud droplets have inertial and make it
into probe
Probe attached
to airplane flying
to left
SO2
Cloud droplets evaporate releasing
SO2 which flows to detector
Some Questions
1.
2.
3.
4.
5.
If it is desired to trap a gas phase analyte in water,
what type of values of Henry’s law constants are
desired?
For desorption of gases from liquids, what type of
values of Henry’s law constants are desired?
How can temperature adjustments be made to
improve Henry’s law constants for trapping or
desorbing gases?
How can trapping of acetic acid in aqueous solution be
improved? What about desorption?
How can trapping of ammonia in aqueous solution be
improved?
Some More Questions
1.
2.
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?
Which component will be enriched in the original solution after
distillation (based on the phase diagram below)?
100
%A
X
100
%
B
Still Mome Questions
3. Based on the phase
diagram to the right, is
it possible to isolate
pure A through multistep/stage distillation
starting from 65% B?
4. Is it possible to isolate
pure B by removing A
through multistep/stage distillation
(starting at same
point)?
T
100% A
X
100% B
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
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
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)
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
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?
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
X(CH3CO2H)
100%
Some Questions From Last Lecture
1.
2.
3.
4.
What are advantages and disadvantages of Soxhlet
extractions?
Suggest a way to isolate a polar organic compound
from ionic compounds in urine.
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?
Can acetic acid be isolated from all solutions in water
by freezing it out?
More Questions
5.
6.
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
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
Liquid-Liquid Extractions
• Partition Coefficient
Kp = [X]raffinate/[X]extractant
• 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
Next Time
• Will cover liquid – liquid extractions from a
quantitative perspective in more detail