Question

(a) Explain how anions and cations can be separated by hydrophilic interaction chromatography in Figure 25-4, using the zwitterion stationary phase in Figure 25-16. Why does the gradient go from ${\mathbf{CH}}_{\mathbf{3}}\mathbf{CN}$.${\mathbf{CH}}_{\mathbf{3}}\mathbf{CN}$to lowcontent?

(b) Explain how the charged aerosol detector used in Figure 26-4 works.

Short answer

We will explain the following in this solution:

1. How cations and anions can be separated by hydrophilic interaction chromatography from figure 26-4 while using the zwitterion stationary phase in figure 25-16.
2. How the charged aerosol detector used in figure 26-4 works.

Step-by-step solution

Definition of zwitterion

1. The stationary phase is hydrophilic with positive and negative charges being fixed in a zwitterion.

Hydrophilic interaction chromatography

• The stationary phase is polar with a layer of aqueous phase on surface.
• The solvent is made more polar than the stationary phase, so it could elute the polar solutes.
• when acetonitrile concentration is decreased eluent strength + eluent polarity increases.

Functions of charged aerosol detector

b. Nebulized effluent aerosol gains charge which is proportional to mass (nonvolatile)

• Fraction of aqueous phase increases; as a result the eluent strength and polarity are increased.
• 20% acetonitrile + 80% aqueous buffer eluent strength is high, so both ions are eluted quickly (ions cannot be separated due to rapid elution).
• 40% acetonitrile + 60% aqueous buffer eluent strength being lower, so both ions are eluted slowly (ions are selectively separated).