Table of Contents
- 1 What does the van Deemter equation tell us?
- 2 What useful information can be found from Van deemter plot?
- 3 Why is the van deemter B term in GC much greater than in HPLC?
- 4 What information is provided by a chromatogram?
- 5 How does temperature affect Van deemter equation?
- 6 Which terms in the van deemter equation contribute the the band broadening in gas chromatography?
What does the van Deemter equation tell us?
The van Deemter equation is a hyperbolic function that predicts that there is an optimum velocity at which there will be the minimum variance per unit column length and, thence, a maximum efficiency. …
What useful information can be found from Van deemter plot?
The useful information that can be found from a Van Deemter plot is B. Optimum mobile phase flow rate.
What is the C term in Van deemter?
The Van Deemter equation is governed by three cumulative terms: (A) eddy diffusion, (B) longitudinal diffusion, and (C) mass transfer. A loss in peak efficiency can be observed as a wider analyte band, and therefore, these three terms can also be viewed as factors that contribute to band broadening.
What is band broadening and what factors can cause it?
The concentration of analyte is less at the edges of the band than at the center. Analyte diffuses out from the center to the edges. This causes band broadening. If the velocity of the mobile phase is high then the analyte spends less time on the column, which decreases the effects of longitudinal diffusion.
Why is the van deemter B term in GC much greater than in HPLC?
8. Why is the van Deemter B term in GC much greater than in HPLC? Diffusion of molecules in the gas phase is much greater than in the liquid phase.
What information is provided by a chromatogram?
Traditional isothermal chromatograms provide useful information about the thermodynamics and kinetics of the analyte-stationary phase interactions and whether these are changing over time. They also provide measures of instrument performance through theoretical plate and tailing factor calculations.
What information can we get from chromatogram?
A paper chromatogram can also be used to identify substances by comparing them with known substances. Two substances are likely to be the same if: they produce the same number of spots, and these match in colour. the spots travel the same distance up the paper (have the same R f value)
What is eddy diffusion in Van deemter equation?
A-term: eddy diffusion: The column packing consists of particles with flow channels in between. Due to the difference in packing and particle shape, the speed of the mobile phase in the various flow channels differs and analyte molecules travel along different flow paths through the channnels.
How does temperature affect Van deemter equation?
Two important consequences of these effects are that as temperature increases, the minimum in the van Deemter equation (Hmin) shifts to higher values of u (21,22) and van Deemter curves flatten (see Figure 3). Thus, elevated temperatures allow for faster separations with little or no loss of efficiency.
Which terms in the van deemter equation contribute the the band broadening in gas chromatography?
Three contributions to the column plate height, H, according to the van Deemter equation. The terms A, B and C are constant for a particular sample compound and a set of experimental conditions. The velocity-independent term A characterizes the contribution of eddy (radial) diffusion to band broadening.
What will decrease the C term in the van Deemter equation?
Which of the following will decrease the C-Term in the van Deemter equation? Decreasing the stationary phase particle diameter in HPLC; Decreasing the column diameter in GC; Decreasing the flow rate. Which type of chromatography uses a liquid stationary phase?