23.1.2 CIA Demonstration: Chromatography

Question 1

CIA Demonstration: Chromatography

Answer 1

• Micropipettes can be created from disposable pipettes.
• Chromatography is a group of procedures for separating components of a mixture.
• The separation in thin layer chromatography (TLC) is based on differences in polarities.

Question 2

note

Answer 2

• Thin layer chromatography (TLC) requires a micropipette to apply the spot of mixture to be separated. Micropipettes can be created from disposable pipettes.
• First, the disposable pipette is heated in the flame of a Bunsen burner. The disposable pipette must be twisted back and forth to ensure uniform heating.
• When the glass is softened, the disposable pipette is removed from the flame and stretched apart. This creates a very thin tube of glass.
• After the tube cools, it is cut into several micropipettes.
• Chromatography is a group of procedures for separating components of a mixture. Types of chromatography include gas chromatography (GC), high performance (or high pressure) liquid chromatography (HPLC), and thin layer chromatography (TLC).
• All types of chromatography involve three basic components. The stationary phase is the support on which the chromatography is performed. For example, filter paper is a stationary phase used in TLC. The mobile phase is the moving solvent front which carries the mixture. For example, water is a mobile phase used in TLC. The substrate is the mixture being separated. For example, grape drink can be separated using TLC.
• The distance moved by a pigment of grape drink is the
  distance from the baseline (where the pigment was applied) to the center of the pigment smear at the end of the chromatography. In this demonstration, the red pigment (lower) moved 38 mm, while the blue pigment (upper) moved 55 mm.
• R f values are calculated by dividing the distance the sample moved by the distance the solvent front moved. R f values of components of a mixture can be compared to known R f values to identify components. For example, if a particular blue pigment has a known R f of 55 mm / 67 mm = 0.82, the blue pigment of grape drink could be identified as that pigment.
• The separation in TLC is based on differences in polarities. Water is a polar molecule, while the molecules making up the filter paper are nonpolar. The blue pigment is more polar than the red pigment, and thus is more soluble in water than on the surface of the filter paper. Therefore, the blue pigment travels further.