chromo: color graph: to write in the mid 1900s used to separate and analyze naturally occurring...
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Chromo: color
Graph: to write
In the mid 1900s used to separate and analyze naturally occurring pigments like those in leaves.
Chromatography
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Real life uses for Chromatography
Law Enforcement – to compare a sample found at a crime scene to samples from suspects
Environmental Agency – determine the kinds of pollutants and level of pollutants
Pharmaceutical Company – determine amount of each chemical found in new product
Hospital – detect levels of chemicals in a patient’s blood stream
Manufacturing Plant – to purify a chemical needed to make a product
Plate: stationary phase
Pigments in the mixture
Solvent: mobile phase
Solvent front
Definition:Chromatography separates components of a
mixture by their distinctive attraction to the mobile phase and the stationary phase.
The mixture looks homogenous before procedure but is made of more than one component
Separates: spreads out for analysis or to make a pure sample
Two phases -- one moves and one stays still
Definition of Chromatography
Phases
Compound is placed on a stationary phase
Made of paper, beads, solid
On Monday made of silica gel plate
Mobile phase passes through the stationary phase
Liquid or gas
On Monday made of solvent 50% acetone/ H2O
Some compounds in mixture spend more time in mobile phase than others and therefore move faster/ farther
What determines how long the pigment spends in the mobile phase?
Polarity
Within covalent molecules, atoms share electrons
If the atoms share equally the molecule is non-polar
Typical of molecules made up of carbon and hydrogen
If the atoms do not share electrons equally,
then portions of the molecule are charged.
These molecules are called polar.
Polarity and Solubility
In general: Like dissolves like
More polar substances dissolve best in polar solvents.
Less polar substances dissolve best in non-polar solvents.
Plate: stationary phase
Pigments in the mixture
Solvent: mobile phase
Solvent front
Molecular View of Chromatography
Stationary phase – molecules are here when they are not dissolved
Mobile phase – molecules are here when they are dissolved
Blue molecules spends the most time in mobile phase because they are the most polar. Red molecules spends the most time in stationary phase because they are the least polar.
D2 = distance to solvent front
D1 = distance to pigment
Rf = D1/D2
= 6.2cm/12.4cm
= 0.5
Rf = retention factor = ratio of distance travelled
Rf is not calculated with
distance between pigments or distance between pigments and solvent front.
Illustration of Chromatography
Components
Affinity to Stationary Phase
Affinity to Mobile Phase
Blue ---------------- Insoluble in Mobile Phase
Black
Red
Yellow
Mixture Components
Separation
Stationary Phase
Mobile Phase
Optimizing information
Concentration of Isopropanol
0% 20% 50% 70% 100%
• Careful choice of solvent and stationary phase.Separation visible at 50%-70%
• View under UV and ambient light to see all pigments.
To make your lab work…
• Mark plate in pencil
• Don’t chip plate
• Avoid getting hand oil on plate
• Spot pigments above level of solvent
• Paper Chromatography – separates dried liquid samples with a liquid solvent (mobile phase) and a paper strip (stationary phase)
• Thin-Layer Chromatography – separates dried liquid samples with a liquid solvent (mobile phase) and a glass plate covered with a thin layer of alumina or silica gel
(stationary phase)
•Liquid Chromatography – separates liquid samples with a liquid solvent (mobile phase) and a column composed of solid beads (stationary phase)
• Gas Chromatography – separates vaporized samples with a carrier gas (mobile phase) and a column composed of a liquid or of solid beads (stationary phase)
•
Types of ChromatographyTypes of Chromatography