L.5 Chromatography

Question 1

Solubility-Based Methods

How do Extractions work?

Answer 1

• Like dissolves like
• Separate desired product

Extraction combines two immiscible (do not mix) liquids, one of which easily dissolves the compound of interest.

The polar (water) layer = Aqueous Phase and dissolves polar compounds

The nonpolar = Organic Phase and dissolves nonpolar compounds.

• Extraction is carried out in a separatory funnel.*
• One phase is collected, and the solvent is then evaporated.*

Question 2

Solubility-Based Methods

What is a WASH?

Answer 2

A wash is the reverse of an extraction, in which a small amount of solute that dissolves impurities is run over the compound of interest.

Question 3

Solubility-Based Methods

Filtration?

Two Types of Filtration?

Answer 3

Filtration isolates a solid (residue) from a liquid (filtrate)

1. Vacuum filtration; the product of interest is solid.
2. Gravity filtration; the product of interest is the filtrate. Hot solvent is used to maintain solubility.

Question 4

Distillation?

Three Types of distillation and when are they used?

Answer 4

Distillation separates liquids with different boiling points. The liquid with the lowest boiling point evaporates first and is collected as the distillate.

1. Simple distillation; boiling points under 150C and are at least 25 apart.
2. Vacuum distillation; Boiling points over 150 to prevent degradation of the product.
3. Fractional distillation; if boiling points are less than 25C apart

Question 5

Chromatography?

Four Types of chromatography?

Answer 5

Chromatography: uses two phases to separate compounds based on their physical or chemical properties.

• Stationary phase or adsorbent; is usually polar solvent
• Mobile phase; runs through the stationary phase and is usually a liquid or gas. This elutes the sample through the stationary phase.

1. Thin-layer and paper
2. Column
3. Gas
4. High-performance liquid

Question 6

Thin-layer Chromatography

3

Answer 6

1. stationary phase = polar material (silica, alumina or paper)
2. mobile phase = non-polar solvent, which climbs the card through capillary action
3. the card is spotted and developed; Rf values can be calculated and compared to reference values.

There is also REVERSE-PHASE CHROMATOGRAPHY

Question 7

Column Chromatography?

Three types of column Chromatography?

Answer 7

Uses polarity, size, or affinity to separate compounds

Stationary Phase is a polar column containing silica or alumina

The mobile phase is a non-polar solvent, which travels through the column by gravity.

1. Ion-exchange chromatography (beads coated with charges)

2. Size-exclusion chromatography (beads with small pores)

3. Affinity Chromatography (beads covered with receptors or antibodies)

Question 8

Gas Chromatography

Answer 8

Gas Chromatography; separates vaporizable compounds according to how well they adhere to the adsorbent in the column.

The stationary phase= coil of crushed metal or a polymer

Mobile phase = nonreactive gas

Can be used in sequence with mass spectrometry

Question 9

High-performance liquid chromatography

Answer 9

HPLC

Similar to, column, uses sophisticated computer-mediated solvent and temperature gradients, It is used if the sample size is small or if forces such as capillary actions will affect results.

Question 10

Retardation Factor Rf

Answer 10

Rf = distance spot moved/ distance solvent moved