a. When preparing a mixture of hexaneacetone mobile phase for a normalphase type LC separation, is it desirable to increase or decrease the proportion of hexane over the course of the separation to elute the more strongly retained analytes faster?

b. Explain why plate heights in LC separations are much smaller than in GC.

c. Which terms in the Van Deemter equation are affected by the following changes to an LC separation. Does the plate height get larger or smaller or is it not possible to determine? Does this make the separation more or less efficient?

i. Decrease particle size

ii. Increase the uniformity of particle size

iii. Increase the flow rate of the mobile phase

iv. Change the composition of the mobile phase to more closely match the properties of the analytes

v. Decreasing the volume of the sample injected

d. What are the molecular characteristics of compounds can be separated by LC but not by GC?

e. When separating an analyte mixture by reversed phase chromatography with 50:50 acetonitrile:water, the peaks are too close together, but elute with values of k = 26. Should you use a higher or lower concentration of acetonitrile to improve the resolution?