Gas Chromatographic Columns
- Page ID
- 284024
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Learning Objectives
All students are expected to:
- Differentiate different types of columns (i.e., WCOT, PLOT, packed), their dimensions, applicability and diffusion factors affecting the separation
- Evaluate suitability of common stationary phases for different analytes
- Distinguish types of interactions between the analytes and stationary phase
- Justify the selection of a stationary phase based on its interactions, stability, and bleed with the targeted analyte
- Evaluate and explain the column bleed
Quiz GC Columns
Provide handwritten answers and bring them to the class
- Compare capillary and packed columns, their dimensions, the common number of theoretical plates, and factors affecting peak broadening.
- Explain the principle and strength of dispersive interactions (London forces), dipole-dipole interactions, hydrogen bonding.
- Differentiate stationary phases and discuss their relationship to the interactions with analytes.
- What is the difference in the interactions with analytes on methyl and phenyl dimethyl polysiloxane stationary phases?
- A homological series of alkanes is analyzed using a linear temperature gradient. What defines the elution order? How does Δtr change for sequentially eluting compounds?
- What are PLOT columns and how are they used?
- What is the column bleed?
- In GC analysis, what is the source of an ion of 207 m/z?
A. Stationary Phases and Integrations in GC
- Match a suitable stationary phase to the following analytes
- List the types of interactions expected between the analytes and stationary phases selected above.
- Which of the stationary phases above would be suitable specifically for GC-MS analysis?
- Which of these stationary phases is the least thermally stable?
B. Separation on PLOT columns
- What are PLOT columns? Please sketch.
- Which of the analytes listed below would be separated on a PLOT column?
- Organic solvents
- Polycyclic aromatic hydrocarbons
- Refinery gases
- Air
- Fatty acids
- Which analytes (of those listed above) would not be suitable for a PLOT column and why?
- Sketch two chromatograms of air on an alumina PLOT column with retention H2< O2 < N2, CO2 using a column with stationary phases of 0.1 µm and 5.0 µm film thickness.
- Would you expect to have longer or shorter retention times on a thicker stationary phase and why?
- How fast would be the elution of the analytes listed above?
- Based on the points 5 and 6 reconsider your chromatograms.
- Would it better work with higher or lower flowrates (Consider Van Deemter theory)
C. GC Analysis and Column Bleed
- Sketch a chromatogram of a solvent (hexane) analyzed using the temperature program from 40 °C to 320 °C with a 25 °C/min gradient.
- What is the column bleed? Consider whether it would affect the sketched chromatogram above?
- Sketch three chromatograms and label all peaks of a series of alkanes (C7-C15) dissolved in n-hexane on a dimethyl polysiloxane stationary phase analyzed using a split injection and
- An Isothermal analysis at 200 °C.
- A temperature program from 40 °C to 320 °C with a 5 °C/min gradient.
- A temperature program from 100 °C to 320 °C with a 5 °C/min gradient.
- Do you expect any co-elution? Why?
D. Optimizing Temperature Program
- The temperature program and analytes elution profile are shown above. How could you modify the temperature program to improve the analysis?
- Determine temperatures at which each analyte eluted in the temperature program used above.
- Is your program shorter or longer than the original?
- Based on questions 2 and 3, reconsider the proposed program and suggest a new one.
Contributors and Attributions
- Alena Kubatova, University of North Dakota (alena.kubatova@und.edu)
- Sourced from the Analytical Sciences Digital Library