Question

1. For a representative 50-cm capillary column operated at 30,000 V, the typical net mobility for a 10-min migration time is about 2x10-8m2V-1s-1. Calculate the number of plates for a small ion, Li+ (D=1.0x10-9m2s-1) and for a 100,000 MW protein with D= 3x10-11 m2s-1.

2. At what pH, 3, or 9, would the electroosmotic flow be faster? Explain why!

3. Order the following species by decreasing total mobility: P3-, S2-, Cl-, K+, Ca2+.

Answer 1

1. Number of theoretical plates in capillary electrophoresis is given by-

For small Li+ ion,

For Protein,

2. The rate of Electroosmotic Flow is dependent on the Electric Field strength and the charge density of the capillary wall. The wall's charge density is proportional to the pH of the buffer solution. The electroosmotic flow will increase with pH, hence at pH 9 the electroosmotic flow would be faster.

3.Electrophoretic mobility is the transport of charged solute in an electric field. Mobility is proportional to q/r ratio.