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Separation of Fullerenes withLiquid Crystal Bonded SilicaPhases in Microcolumn High
Performance Liquid
ChromatographyYoshihiro Saito, Hatsuichi Ohta,Hideo Nagashima, Kenji Itoh,
and Kyokatsu Jinno
A report by
L. Lao, R. Lopez, K.M.P. Palmario, and S. Sibug
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What are Fullerenes?
third allotropic form of carbon material(after graphite and diamond)
molecules composed entirely of carbon,
in the form of a hollow sphere, ellipsoid,or tube
similar in structure to graphite, which iscomposed of a sheet of linked
hexagonal rings, but they containpentagonal (or sometimes heptagonal)rings that prevent the sheet from beingplanar
Also ver lar e PAHs
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Polycyclic AromaticHydrocarbons
Potent atmospheric pollutants thatconsist of fused aromatic rings anddo not contain heteroatoms or carry
substituents (example: naphthalene) Produced as by-products of fuel
burning; found in cooked food; found
in meteorites Lipophilic
Formed from incomplete combustionofcarbon-containing fuels
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Microcolumn HPLC
Advantages Lesser reagent and starting material Greatly enhanced sensitivity. Dramatic solvent savings, without altering
the resolution and retention values. Ideal for applications in which very small
quantities of samples are available foranalysis.
Favorite choice for applications in LC/MS. Better choice for applications in drug
discoveries and screening. Ideal for applications in genomics and
proteomics.
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Octadecylsilane-Bonded SilicaStationary Phases
Commonly used as stationary phasefor separation of fullerenes
May be monomeric or polymeric have different mol shape and sizerecognition capability
Retention
Resolution
Elution order
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Liquid Crystal Bonded SilicaPhases
Liquid crystals generally of HMW and lowvolatility; ordered fluid mesophase of a longchain molecule with both solid-like molec.
order and liquid-like character Intermediate between solid and true
isotropic liquid
Advantage: Reduces or eliminates column-
bleed
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Objectives of the Study
To be able to separate C60 and C70fullerenes using liquid crystal silicabonded phases in HPLC
To be able to perform micro-columnHPLC
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Methodology
Syntheses and basic characteristicsof the bonded phases. Determination of surface coverage values of
these bonded phase used specific area of theoriginal silica gel and carbon content of these
bonded phases.
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Methodology
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Methodology
Chromatographic measurements.
the synthesized bonded phases werepacked using a slurry method.
The mobile phases were prepared fromguaranteed reagent grade n hexane,toluene,and dichloromethane.
Chromatographic measurements weredone at least 5 times.
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Methodology
PAH sample
used for evaluationin this investigation
were commerciallyavailable. Except TBN and
PhPh.
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Results and Discussion
Separation ofC60and C70 with two
liquid crystal
bonded silicaphases
n-hexane as themobile phase for the
evaluation of thebasic separationperformance of theliquid crystal
phases.
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Results and Discussion
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Effect of mobile phase composition onfullerene Separation
Using n-hexane/dichloromethaneand n-hexane/toluene asmobile phase
Smaller capacity factorswith increasingdichloromethane andtoluene
Better peak shapes ofchromatogram observedusing n-hexane/toluene
Due to increased solubility
of C60 and C70 in themobile phase
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Effect of mobile phase composition onfullerene Separation
Liquid crystal phase anda mobile phase withtoluene up about to 42% Can be used to obtain
the same separation
factor as ODS-5 (1.84)
Advantageous feature Better solubility
greater sampleloadability
Other good solventshaving greaterdissolution power can beused as mobile phase
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Effect of columntemperature
PAHs:
- k decreases withincreasing temperature- Normal temperaturebehavior observed
fullerenes:- k increases withincreasing temperature
- Selectivity slightlydecreases with increasing
temperature
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Effect if columntemperature
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Effects of columntemperature
Values forenthalpy oftransfer suggestthat the PAHs and
fullerenes havedifferent retentionmechanisms
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Molecular shape recognition
Previous study (Saito, 1994)evaluated molecular shaperecognition capabilities of liquid
crystal bonded phase with PAHs assample probes
Results indicated:
Liquid crystal phase had better planarityand shape recognition power than ODS
Selectivity significantly decreased with
increasing temperature
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Molecular shape recognition
Results indicatedecrease inplanarrecognitioncapability ofliquid crystalphase 1 with
increasing
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Molecular shape recognition
Results indicate thatmore elongated PAHsshow larger decrease inretention with increasingtemperature
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Molecular shape recognition
At elevated column temperature,phase ordering of liquid crystalsreduced by their thermal mobility
slot-like structure (ligandinterval that is smaller thanmolecular sizes of fullerenes)
At elevated temperatures, slot-likestructure is lost
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Proposed interaction modelPlanar, rod-like
NonplanarFullerenes
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Conclusion
At low temp, planar rod-like PAHsinteract effectively with the bondedphases = ordered structure
Nonplanar molecules cannot interact aswell
Fullerenes C60 have longer retentionthan PAHs at higher temp
Ligand interval increases as tempincreases Interaction between C60 and bonded phase is
easier
Results indicate possible effective