1. Chem. 230 – 9/2 Lecture

2. 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

3. Introduction - Students
Introduce yourself (name/degree plan)
Is there anything specific you expect to get out of the class?

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

5. 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)

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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 12

13. 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). 13

14. 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.

15. Separation Purposes Isolation/Purification/Removal of Compound(s)
Qualitative Analysis
Quantitative Analysis

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

17. Simple Separations/Extractions - Introduction
Assigned text reading:
p. 1-26: light, background reading
p : 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)

18. 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

19. Simple Separations - Examples of Strategies
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.

20. 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)

21. 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

22. 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)

23. 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

24. 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

25. 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

26. 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

27. 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

28. 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
100% A Xi
100% B
Azeotropic mixture P
100% A Xi
100% B

29. 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

30. Some Questions
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?

31. Some More Questions
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)? X
100% A
100% B

32. 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
100% A X
100% B

33. 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

34. 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

35. 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)

36. 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

37. 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?

38. 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
100%
X(CH3CO2H)

39. Some Questions From Last Lecture
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 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?

40. 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 , calculate the total NH3 concentration in the sample 40

41. 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 41

42. 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 42

43. Next Time
Will cover liquid – liquid extractions from a quantitative perspective in more detail 43