Chromatography Chromo: color Graph: to write In the mid 1900s used to separate and analyze naturally occurring pigments like those in leaves. year7hawkesdale.wikispaces.com

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

Solvent front Plate: stationary phase Pigments in the mixture Solvent: mobile phase

Definition of Chromatography 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

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.

Solvent front Plate: stationary phase Pigments in the mixture Solvent: mobile phase

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 Rf is not calculated with distance between pigments or distance between pigments and solvent front. D1 = distance to pigment Rf = D1/D2 = 6.2cm/12.4cm = 0.5 Rf = retention factor = ratio of distance travelled

Illustration of Chromatography Stationary Phase Separation Mobile Phase Mixture Components Components Affinity to Stationary Phase Affinity to Mobile Phase Blue ---------------- Insoluble in Mobile Phase Black         Red      Yellow          

Optimizing information Careful choice of solvent and stationary phase. Separation visible at 50%-70% View under UV and ambient light to see all pigments. 0% 20% 50% 70% 100% Concentration of Isopropanol

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

Types of Chromatography 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)