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Chromatography is a process whereby the |
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purity
of a sample may be determined. |
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the components of a mixture may be separated |
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the separated components may be identified |
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A sample that requires analysis is often a
mixture of many components in a complex matrix. |
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Often a standard containing either a single pure
compound or a mixture of known amounts of several compounds will be used
for comparison with the test sample and the chromatograms compared. |
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A mixture can be separated using the differences
in physical or chemical properties of the individual components |
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spaghetti from the water in which it was cooked |
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filtering to separate a ppt from a liquid |
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based on the states of matter of the two
components, |
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also useful for separations are density and
size. |
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useful
chemical properties by which compounds can be separated are solubility,
boiling point, and vapor pressure. |
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Chromatography is a separations method that
relies on differences in partitioning behavior between a flowing mobile
phase and a stationary phase to separate the the components in a mixture. |
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A column holds the stationary phase and the
mobile phase carries the sample through it. |
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Sample components that partition strongly into
the stationary phase spend a greater amount of time in the column and are
separated from components that stay predominantly in the mobile phase and
pass through the column faster. |
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Gas chromatography (GC) |
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Applied to volatile organic compounds. The
mobile phase is a gas and the stationary phase is usually a liquid on a
solid support or sometimes a solid adsorbent. |
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High-performance liquid chromatography (HPLC) |
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A variation of liquid chromatography that
utilizes high-pressure pumps to increase the efficiency of the separation. |
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Liquid chromatography (LC) |
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Used to separate analytes in solution including
metal ions and organic compounds. The mobile phase is a solvent and the
stationary phase is a liquid on a solid support, a solid, or an
ion-exchange resin. |
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Size-exclusion chromatography (SEC) |
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Also called gel-permeation chromatography (GPC),
the mobile phase is a solvent and the stationary phase is a packing of
porous particles. |
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Thin-layer chromatography (TLC) |
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A simple and rapid method to monitor the extent
of a reaction or to check the purity of organic compounds. The mobile phase
is a solvent and the stationary phase is a solid adsorbent on a flat
support. |
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Paper chromatography (PC) |
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This is the simplest form of chromatography. |
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The stationary phase is a special chromatography
paper. |
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The mobile phase is a solvent mixture, e.g.
water and ethanol. Trial and error establishes the best solvent for good
resolution. |
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A gas chromatograph consists of a flowing mobile
phase, an injection port, a separation column containing the stationary
phase, and a detector. |
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The organic compounds are separated due to
differences in their partitioning behavior between the mobile gas phase and
the stationary phase in the column. |
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Mobile phases are generally inert gases such as
helium, argon, or nitrogen |
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The injection port consists of a rubber septum
through which a syringe needle is inserted to inject the sample. |
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Separate documents describe some specific GC Columns and GC Detectors. |
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The mobile phase can be a polar liquid, which
moves slowly through the column. |
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HPLC can
be used to separate components unsuited to GC |
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is suited to preparing relatively large
quantities of a pure compound or identifying the presence of very small
quantities. |
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Liquid chromatography (LC) is an analytical chromatographic
technique that is useful for separating ions or molecules that are
dissolved in a solvent |
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Conventional LC is most commonly used in
preparative scale work to purify and isolate some components of a mixture. |
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It is also used in ultratrace separations where
small disposable columns are used once and then discarded. |
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Used to separate analytes in solution including
metal ions and organic compounds. |
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The mobile phase is a solvent and the stationary
phase is a liquid on a solid support, a solid, or an ion-exchange resin. |
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Thin-layer chromatography (TLC) is a chromatographic
technique that is useful for separating organic compounds. |
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it is often used to monitor the progress of
organic reactions and to check the purity of products |
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Thin-layer chromatography consists of a
stationary phase immobilized on a glass or plastic plate, and an organic solvent. |
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The sample, either liquid or dissolved in a volatile solvent, is
deposited as a spot on the
stationary phase |
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The constituents of a sample can be identified
by simultaneously running standards with the unknown. |
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The bottom edge of the plate is placed in a
solvent reservoir, and the solvent moves up the plate by capillary action.
When the solvent front reaches the other edge of the stationary phase, the
plate is removed from the solvent reservoir. |
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The separated spots are visualized with
ultraviolet light or by placing the plate in iodine vapor. |
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The different components in the mixture move up
the plate at different rates due to differences in their partioning
behavior between the mobile liquid phase and the stationary phase. |
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The mobile phase is a solvent mixture, e.g.
water and ethanol. Trial and error establishes the best solvent for good
resolution. |
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The mixture under analysis is placed in a tiny,
concentrated dot near the bottom of the paper. |
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The paper is hung with the bottom dipped in
solvent, which rises up the paper to come in contact with the mixture. |
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As the solvent rises further up the paper, the
components are separated as they are swept along. |
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The strip of paper is called a chromatogram. |
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Identification of the components is based on Rf
values – a ratio between the distance traveled by the component to the
distance traveled by the solvent front. |
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Introduction to Chromatography Using TLC |
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Column Chromatography and Grape Kool-Aid |
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Gasoline Analysis Using Gas Chromatography |
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http://www.chem.vt.edu/chem-ed/ac-basic.html |
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http://www.usm.maine.edu/~newton/TANES/TLCAPP.HTML |
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http://www.state.ia.us/government/dps/dci/lab/drugchem/drugchem.htm |
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http://www.wellesley.edu/Chemistry/chem211lab/Orgo_Lab_Manual/Appendix/Techniques/TLC/thin_layer_chrom.html |
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http://www.wpi.edu/Academics/Depts/Chemistry/Courses/CH1010/Stream1/tlc.html |
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Notes