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)

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Types of ChromatographyTypes of Chromatography