Shown below are three van Deemter curves for columns containing a microporous stationary phase with particle diameters of 5 um, 3 μm, and 1.8 μm. Why does the van Deemter curve shift downward as the particle size decreases? Decreasing the particle size results in more possible paths through which the solvent can flow, which increases the contribution of the A term to the plate height. At constant pressure, the flow rate through the column decreases as the particle size decreases which increases the contribution of the B term to the plate height. As the particle size decreases, the flow through the column becomes more uniform which reduces the contribution of the A term to the plate height. As the particle size decreases, the analyte spends more time in the stationary phase which increases the contribution of the C term to the plate height. O Once the particle size is small enough, the equilibration time between the mobile and stationary phases becomes very rapid which reduces the contribution of the C term to the plate height. Plate height (um) 18 16 6 2 5 μm 3 μπ 1.8 μm 024 6 8 Linear flow rate (mm/s) 10

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Chapter1: Chemical Foundations
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Shown below are three van Deemter curves for columns containing a microporous stationary phase with
particle diameters of 5 um, 3 um, and 1.8 μm. Why does the van Deemter curve shift downward as the
particle size decreases?
Decreasing the particle size results in more possible paths
through which the solvent can flow, which increases the
contribution of the A term to the plate height.
At constant pressure, the flow rate through the column
decreases as the particle size decreases which increases
the contribution of the B term to the plate height.
As the particle size decreases, the flow through the column
becomes more uniform which reduces the contribution of
the A term to the plate height.
As the particle size decreases, the analyte spends more
time in the stationary phase which increases the
contribution of the C term to the plate height.
Once the particle size is small enough, the equilibration
time between the mobile and stationary phases becomes
very rapid which reduces the contribution of the C term to
the plate height.
The pressure required to push solvent through the column
increases as the particle size decreases. Higher pressures
mean the analyte spends less time in the column which
reduces the contribution of the B term to the plate height.
Plate height (um)
18
16
8 +
4+
2
02
5 μm
3 μm
1.8 μm
4 6
8
Linear flow rate (mm/s)
10
Transcribed Image Text:Shown below are three van Deemter curves for columns containing a microporous stationary phase with particle diameters of 5 um, 3 um, and 1.8 μm. Why does the van Deemter curve shift downward as the particle size decreases? Decreasing the particle size results in more possible paths through which the solvent can flow, which increases the contribution of the A term to the plate height. At constant pressure, the flow rate through the column decreases as the particle size decreases which increases the contribution of the B term to the plate height. As the particle size decreases, the flow through the column becomes more uniform which reduces the contribution of the A term to the plate height. As the particle size decreases, the analyte spends more time in the stationary phase which increases the contribution of the C term to the plate height. Once the particle size is small enough, the equilibration time between the mobile and stationary phases becomes very rapid which reduces the contribution of the C term to the plate height. The pressure required to push solvent through the column increases as the particle size decreases. Higher pressures mean the analyte spends less time in the column which reduces the contribution of the B term to the plate height. Plate height (um) 18 16 8 + 4+ 2 02 5 μm 3 μm 1.8 μm 4 6 8 Linear flow rate (mm/s) 10
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