Separation of analytes

Separation of analytes - context
Analyte mixtures and separation - 1
Analyte mixtures and separation - 2
Analyte mixtures and separation - 3
Introduction to chromatography
Chromatographic columns
Principle setup of a chromatographic unit
Example of separation
Chromatographic system - 1
Chromatographic system - 2
Standard gas chromatograph
(Old) liquid chromatography unit
(New) liquid chromatography unit
HPLC columns
Comparison GC and HPLC
Selftest
     1) Purpose of chromatographic process
           Answer
     2) Unsuitable compounds
           Answer
     3) HPLC vs. GC
           Answer
     4) Detectors
           Answer
     5) Solvent properties
           Answer
     6) Retention time
           Answer
     7) Analyte identification
           Answer
     8) Irreversible or reversible sorption process
           Answer
     9) Short analysis time
           Answer
     10) Short analysis time
           Answer
     11) Breakthrough-curve
           Answer
Problems
End of lesson

11) Breakthrough curve

 

Question:

Change the excel sheet chromatography.xls such that it applies to a filtration rather than a chromatographic process. You will find that the calculation of the modified excel sheet will yield an elution profile that resembles the breakthrough-curve shown in Figure 40 in the script.

Note: This excel sheet does not explicitly calculate any diffusion or dispersion.
Hence, the calculated result should actually have been a step function from Cout=0 to Cout=Cin at t=tir instead of a smooth breakthrough-curve.
Why is the calculated BTC smoother than it should be?

 

Answer:

The smoothing is a mathematical artifact that arises from the temporal and spatial discretization of the transport and sorption processes. This artifact is called 'numerical dispersion' as it affects the calculated BTC much in the same way as real diffusion and dispersion affect real breakthrough-curves. In more sophisticated models, numerical dispersion is corrected for.