Questions:

1) Why is it advantageous to use zwitterionic stationary phase compared to other liquid chromatography stationary phase discussed in this class?  And why it might be disadvantageous?

2) Using the sulfobetaine stationary phase, would cations or anions be retained more strongly?

3) A chemist was analyzing oligomers of a protein using HILIC/CEX with an ELS detector. The detector showed the most response to the later eluting peaks. What can be said about the average size of oligomer the protein forms?

4) List three factors that can affect selective and retention using a zwitterionic column.

Answers:

1) Separation of cations/anions and neutral analytes all at once on the same column. Disadvantage: Complicated sample because might co-eluted and variety of ion-paring possibility

2) Anions

3) The protein on average forms larger oligomers.  [Instructor comment:  not clear if you are discussing protein oligomers – non-covalently bonded peptides stuck together – or amino acid oligomers.  I’m assuming it meant amino acid oligomers or peptides] 

4) Ionic strength, pH, make-up of the mobile phase, interaction of others analytes in sample, types of surfactant used