# Introduction to Chromatography Homework Problem Set

This problem set was developed by S.E. Van Bramer for Chemistry 366 at Widener University.

## Goal:

To introduce students to chromatographic separations

## Objectives:

• Students will be familiar with terms commonly used for chromatographic separations
• Students will understand the variables used to describe chromatographic performance
• Students will understand the effect of changing instrument parameters on chromatographic performance
• Students will be able to describe how separation occurs in gas and liquid chromatography

## Retention

1. Describe the function of the stationary phase and the mobile phase.
2. Describe the relationship between the mobile phase flow rate and the linear velocity for both open tubular and packed columns.
3. For a chromatographic separation with the following retention times: Mobile phase 30.0 s, Compound A 60.0 s; Compound B 75 s. Determine the adjusted retention time for each compound, the retention factor for each compound, and the selectivity factor for the column.
4. For this chromatographic system, predict the retention time for a compound with a retention factor of 1, 5, and 10.
5. What happens to the retention time for a compound if the equilibrium between the stationary and mobile phases, Kc, increases?
6. What happens to the retention time for a compound if the volume of the stationary phase increases?
7. What happens to the retention time for a compound if the volumetric flow rate increases?

1. The peak width at half height in the above analysis for; A = 0.50 s and B = 0.54 s. If the separation is with a 15 cm column, determine the number of theoretical plates and the theoretical plate height.
2. Calculate the resolution for this separation.
3. If the number of theoretical plates is doubled, what happens to the resolution for this separation.

## Band Theory

Given the equation: H = A + B/u + Csu+ CM u
1. Explain the effect of increasing the mobile phase flow rate. What are the tradeoffs and how is this parameter optimized?
2. Explain the effect of reducing the stationary phase thickness. What are the tradeoffs and how is this parameter optimized?
3. Explain the effect of reducing the column diameter. What are the tradeoffs and how is this parameter optimized?
4. For a packed column, explain the effect of reducing the size of the packing material. What are the tradeoffs and how is this parameter optimized?
5. Explain the effect of increasing the column length. What are the tradeoffs and how is this parameter optimized?
6. Explain the effect of changing the temperature. What are the tradeoffs and how is this parameter optimized?
7. Explain the effect of changing the solvent. What are the tradeoffs and how is this parameter optimized?

Please send comments or suggestions to svanbram@science.widener.edu

Scott Van Bramer
Department of Chemistry
Widener University
Chester, PA 19013