Chromatography

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  • Created by: aarafa11
  • Created on: 24-09-18 10:17
How does TLC separate molecules
Absorbtion
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What is the 2 mechanism for separation in chromatography
1) Partition 2) Absorbtion
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How to analyse TLC chromatography to identify compound
measure the solvent font and how far the spot traveled to calculate the Rf value. Compare the Value to known data
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What is the problem with compounds that have similar Rf value
Similar compounds will have similar Rf value
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How gas chromatography and mass spectrometer contribute to the analysis
Gas chromatography sepeartes the mixture, mass spec produces a distinctive fragmentation pattern so we can identify it on known data
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Define Rf value
is distance moved by a spot / distance moved by solvent
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Define retention time
is the time between injection and or detection of a component
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What is the role of the gas in chromatography
its the mobile phase
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What is the role of the liquid in chromatography
its the stationary phase
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gas/liquid chromatogram could be used to determine the percentage composition
%= (area of 1 peak/total area under each peak) x 100
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what happens when both stationary and mobile phase are liquid
the rate of movement of each solute depends on its relative solubility in the 2 phases
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what phase is solutes more soluble in
in mobile phase as it moves faster and leaves the column first
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Define adsorbtion
solutes are held on the surface of STATIONARY phase
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in adsorbtion, why is it in the stationary phase
it is a polar solid and the solutes is polar
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what causes the solutes to be adsorbed more and why?
by the difference in polarity as it separates the solutes more
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Define eluent
its the mobile phase that helps move the substance along the stationary phase
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what is the stationary phases in Gas chromatography
liquid absorbed onto the surface of inert material
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what is the mobile phases in Gas chromatography
inert gas (N2 or He)
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what is the stationary phases in TLC
silica gel/ Al2O3 coated in inert support
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what is the mobile phases in TLC
liquid solvent
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what is the stationary phases in normal HPLC phase
silica particles (POLAR)
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what is the mobile phases in normal HPLC phase
NON POLAR solvent (hexane)
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what is the stationary phases in reversed HPLC phase
silica particles with long hydrocarbons attached (NON POLAR)
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what is the mobile phases in reversed HPLC phase
POLAR SOLVENT (water/ methanol mixture)
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if a compound is more polar than the other, which HPLC phase do you use
reversed HPLC - theres a strong attraction between poloar molecules and solvent
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What are the condition for HPLC
high pressure 400atm
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What is the advantage of HPLC
can use small patricle size = larger SA = for interaction = better seperation
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The method of gas chromatography
Sample injected is vapourised. Carried through column by inert gas. Liquid in column (stationary phase) absorbed onto inert solid. At different detention time, detectors will compare data
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Define inert
wont react with molecules
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limitation of TLC
Siliar compunds will have similar Rf. Unknown compound has no reference. may be difficult to find solvent to separate
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How to find th concentration of compound
Standard solution of known conc. Gas chrom for each standard. plot calibration curve. Obtain UNKNOWN gas chrom under same condition. Use curve to measure conc
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limitation of gas chromatography
chemicals have high chance of having same retentiontime, peak shape and detection response. Not all sample will be separated so it'll hide beneath substance that has higher conc and same retention time. known substance have no reference
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What are the stages of mass spectrometer
1) ionisation 2) acceleration 3) deflect 4) detect
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Other cards in this set

Card 2

Front

What is the 2 mechanism for separation in chromatography

Back

1) Partition 2) Absorbtion

Card 3

Front

How to analyse TLC chromatography to identify compound

Back

Preview of the front of card 3

Card 4

Front

What is the problem with compounds that have similar Rf value

Back

Preview of the front of card 4

Card 5

Front

How gas chromatography and mass spectrometer contribute to the analysis

Back

Preview of the front of card 5
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