Multidimensional GC separations (advanced course 1/1)

Jiri G. K. Sevcik, Dept. Analytical Chemistry, Charles University Prague

 

Syllabus

1. Definitions:

discussion of parameters of retention equations,

- separation efficiency, factors affecting the profile broadening,

- resolution efficiency – separation number, statistical model of peak overlap,

- relevance of information - ultimate uncertainty, information content, additivity of probabilities, hyphenation.

2. Chromatographic dimension:

definition in terms of a constant value of a retention factor,

- retention factor change,

- - continuous – gradient chromatography,

- - stepwise change – hyphenation.

3. Separation:

solvation – weak interactions,

- Abraham’s equation – LSER model of solvation,

- - solute descriptors (in LSER calculations based on molecular properties, QSPR),

- - independence of solvent properties (LSER parameters, methods of MLRA),

- solute/solvent interactions (multiplication),

- retention as an additive function of interactions, prediction of retention behaviour, optimization of stationary phase selection.

4. Selectivity:

stationary phases,

- quantitative description, classification criteria,

- - LSER equation parameters, r, s, a, b - tailored stationary phases,

- optically active solutes – enantioselective phases,

- biologically active solutes - imprinted stationary phases.

5. Hardware in multiple column techniques:

switching valves, valveless designs,

switching modes,

optimization criteria, information content, information flow, cost of information.

6. High performance systems:

elution profile changes, exponential modification due to

- extracolumn effects, dead volume, internal diameters of connections, duration of stop flow period, diffusion coefficient, starting peak width,

efficiency drop of a tandem system due to a previous step.

7. Recycle chromatography in capillary column systems:

stationary phase selection for precolumn and loop,

loop in-line detector,

separation of isomers.

8. Orthogonal systems:

columns in series,

- comprehensive chromatography with

- - thermo-modulation,

- - multiple sample injection - chopping,

- - heartcut, peak deconvolution,

precision of retention data, data banks.

9. Combinatorial systems:

parallel columns with sequential identification,

- parallel columns with pre/separation, selection of optimum stationary phases and the number of columns,

identification matrix comprising retention time and signal value,

- microTCD with short capillary columns,

a low value of ultimate uncertainty in an IF-THEN-AND-AND....-AND logic chain.

10. Three instrumental principles aimed at a reduction of the ultimate uncertainty:

nanotechnology for multidimensional separations,

multiple column systems with integrated detectors,

dedicated systems, expert systems.

Important topics to be mastered prior to the beginning of the advanced course ”Multidimensional GC separation”

Jiří G.K.Ševčík
  1. Characterize the weak interactions participating in the separation process and list them in the order of decreasing magnitude. What are their units?
  2. Which type of interaction determines the selectivity of a separation process?
  3. Which term in van Deemterś equation exerts the main effect on the duration of a separation?
  4. How will HETP change with changing speed of separation?
  5. The ways of speeding up separation processes?
  6. In which way the mobile phase influences the separation process?
  7. What is the impact of the stationary phase on separation processes?
  8. Which quantitative parameters describe the separation process?
  9. What is more important for analyte characterization: absolute or relative retention data?
  10. Is the probability of analyte identification improved more by a good repeatability of the retention time measurement or by an increased number of theoretical plates?
  11. What is the ultimate uncertainty and in which way is it expressed?
  12. If the ultimate uncertainty is expressed in terms of the separation number value of 10 and is to be improved by a factor of two, what will be the separation number value and how it can be attained?
  13. In which way is the separation influenced by the system selectivity and efficiency?
  14. How will a separation change when using a short apolar and polar precolumn?
  15. If the retention order is A<B=C on an apolar column, what will be the retention order on a polar column?
  16. To achieve a separation, is it better to use a 50 m long single column or to connect two 25 m long columns in series? Give the reasons and specify the conditions.
  17. How the sample separation changes when using systems with apolar and polar columns of the same efficiency? Give the reasons and specify the conditions?
  18. What principles are used to maintain a constant flow of a mobile phase? Draw a schematic for all the three approaches.
  19. What type of flow regulation will provide a constant, temperature independent flow?
  20. Is the duration of analysis in a temperature program mode dependent on the flow regulator type? With which type it will last longer?
  21. Is the analyte signal a function of the experimental separation conditions? Give quantitative relationships.
  22. Which data handling parameters are essential for peak identification?
  23. What are the limiting factors of multidimensional separation systems and how their effects can be reduced?
  24. What are the advantages of multidimensional separation systems and how can they be quantified?