CHM 256-CHAPTER 7

Helium, nitrogen and argon are classified under which phase in chromatography?

• Stationary phase

• Mobile phase

In a normal-phase chromatography system using silica gel as the stationary phase and a mixture of hexane, ethanol, and methanol as the mobile phase, which solvent would likely be eluted first?

• Silica gel

• Hexane

• Ethanol

• Methanol

Octadecylsilane (C18), consisting of 18-carbon alkyl chains bonded to silica, is a common stationary phase in reversed-phase chromatography. If the mobile phase contains a mixture of isopropanol and hexane, which solvent would be more strongly retained by the C18 stationary phase?

• Hexane

• Isopropanol

• Distilled water

• Octadecylsilane

Definition: the stationary phase is a solid. Separation is due to a series of adsorption/desorption steps. Which chromatography term refers to this definition.

• Paper chromatography

• Thin-layer chromatography

• Partition chromatography

• Adsorption chromatography

Nitrogen, helium and argon are examples of mobile phases used gas chromatography. Classify these mobile phases according to chromatography term.

• Elution

• Eluent

• Eluate

Match the situation below with the correct chromatography term: Eluent

• Ethanol is used as a mobile phase and solvent to determine the composition of dye mixtures.

• The distance from start to centre of substance spot is 5 cm whereas the distance from start to solvent front 7 cm

• A mixture of water, acetonitrile, and formic acid is used as a mobile phase to elute compounds through a silica bed (stationary phase)

Specify the type of thin layer chromatography?

• Adsorption chromatography

• Partition chromatography

A mixture of compounds containing different functional groups, including hydroxyl and alkyl groups, was analyzed using TLC (thin-layer chromatography). It was found that the retention factor (Rf) for compounds with alkyl groups is 0.77, whereas the Rf for compounds with hydroxyl groups is 0.44. Which of the following statements is correct for this experiment?

• Alkyl group has stronger interaction with silica (stationary phase) and move slowly with the mobile phase. Alkyl group will elute later

• Hydroxyl group has stronger interaction with silica (stationary phase) and move rapidly with the mobile phase. Hydroxyl group will elute first

• Hydroxyl group has stronger interaction with silica (stationary phase) and move slowly with the mobile phase. Hydroxyl group will elute later

• Weak interaction between alkyl group and silica (stationary phase) and alkyl group move slowly with the mobile phase.

A postgraduate student used sulphuric acid to develop black spot in a mixture of compounds and employed a planar chromatography technique to separate them. However, after some time, the student realized that his technique was incorrect because the chromatography method he chose was incompatible with sulphuric acid. Determine which type of chromatography the student likely used.

• Paper chromatography

• Thin layer chromatography

• Ion exchange chromatography

• column chromatography

Why blue colour compound eluted first than yellow colour compound?

• Blue colour compound has a strong affinity towards the stationary phase. Yellow has less affinity for the stationary phase

• Yellow colour compound has a strong affinity towards the stationary phase. While, blue colour compound has less affinity for stationary phase