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

Based on Partitioning

Non-Partitioning

Higher Resolution/Instrument Based

FilteringLiquid-liquid extraction

Gas ChromatographyCapillary Zone Electrophoresis

Simple separations

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. 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.

Simple Separations

• Almost all separations require more than one discrete phase

• The most common separations involve partitioning between two phasesX(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 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

Types of Simple Separations

Phases ExamplesGas - 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

• Gas Sampling– Bubblers– Mist Chambers

(show)– Denuders(above for water

soluble gases)

– Cold Traps

Bubbler

Denuder

Sample Air

To filter, pump

Gases trapped on wall coating

Aerosols pass to filter

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

liquid

Headspace

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 inHe to waste

Trapped analyte

He in

To GC

Heat applied

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

• 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

Xi100% A 100% B

P

Xi100% A 100% B

Liquid

VaporV + L

A is more volatile (lower Tb)

Azeotropic mixture

Simple Separations – Gas/Liquid

• Many other separations possible

• Unusual Separation: Analysis of dissolved SO2 in cloud water (my dissertation project)

Counter-flow Virtual Impactor

Scrubbed air goes to tip and splits into 2 flows

Probe attached to airplane flying to leftCounter flow out of probe

tip keeps gaseous SO2 out

SO2

Cloud droplets have inertial and make it into probe

Cloud droplets evaporate releasing SO2 which flows to detector

SO2

Some Questions

1. If it is desired to trap a gas phase analyte in water, what type of values of Henry’s law constants are desired?

2. For desorption of gases from liquids, what type of values of Henry’s law constants are desired?

3. How can temperature adjustments be made to improve Henry’s 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?

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)?

X100% A

100% B

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

X100% A 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 SO4

2- 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

X(CH3CO2H)0 100%

TEutectic Point

Ice + CH3CO2H (l)

CH3CO2H(s) + H2O(l)

Liquid solution

Solid solution

Liquid “path” for cooling 50% acetic acid in water

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 [CO3

2-] = 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?

More Questions5. 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 mol 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?

6. 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