Exploring Chemical Analysis
Exploring Chemical Analysis
5th Edition
ISBN: 9781429275033
Author: Daniel C. Harris
Publisher: Macmillan Higher Education
Question
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Chapter 22, Problem 22.5P

(a)

Interpretation Introduction

Interpretation:

Number of plates and plate height and resolution has to be calculated.

Concept Introduction:

Expression to compute number of theoretical plate is as follows:

  N=5.55 tr2w1/22

Here,

tr denotes analyte’s  retention time.

w1/2 denotes peak width at half-height.

N denotes number of theoretical plate.

It has been found that greater the equilibration steps narrower will be band so this suggests N should be high for more resolution or narrower separation.

Expression to compute plate height is as follows:

  H=LN

Here,

N denotes number of theoretical plate.

L denotes length of chromatographic column.

H denotes plate height.

(a)

Expert Solution
Check Mark

Explanation of Solution

Expression to compute number of theoretical plate is as follows:

  N=5.55 tr2w1/22        (1)

Substitute 50 min for tr and 0.263 mm  for w1/2 in equation (1).

  N=5.55 (50 min )2(0.263 mm )2=2×105

Thus, number of theoretical plate is 2×105.

Expression to compute H from number of plates from is as follows:

  H=LN        (2)

Substitute 100 m for L and 2×105 for N in equation (2).

`

  H=(100 m2×105)(1000 mm1 m)=0.50 mm

Thus, plate height is 0.50 mm.

Value of Δtr is calculated as follows:

  Δtr=63.5 min63 min=0.5 min

Expression to compute resolution is as follows:

  Resolution=Δtrwavg        (3)

Substitute 0.5 min for Δtr, 0.384 min for wavg in equation (3).

  Resolution=0.5 min0.384min=1.3

Thus, value of resolution is 1.3.

Ratio of plate height is calculated as follows:

  Plate height in liquid chromatographyPlate height in gas chromatography=(10 μm0.50 mm)(1 mm1000 μm)=150

Reason behind such massive plate height difference is that rate of longitudinal diffusion is much more rapid in gas than in liquid chromatography.

(a)

Interpretation Introduction

Interpretation:

Number of plates and plate height for peak 11 and resolution for peaks 16 and 17 has to be calculated.

Concept Introduction:

Expression to compute number of theoretical plate is as follows:

  N=5.55 tr2w1/22

Here,

tr denotes analyte’s  retention time.

w1/2 denotes peak width at half-height.

N denotes number of theoretical plate.

It has been found that greater the equilibration steps narrower will be band so this suggests N should be high for more resolution or narrower separation.

Expression to compute plate height is as follows:

  H=LN

Here,

N denotes number of theoretical plate.

L denotes length of chromatographic column.

H denotes plate height.

(a)

Expert Solution
Check Mark

Explanation of Solution

Expression to compute number of theoretical plate is as follows:

  N=5.55 tr2w1/22        (1)

Substitute 50 min for tr and 0.263 mm  for w1/2 in equation (1).

  N=5.55 (50 min )2(0.263 mm )2=2×105

Thus, number of theoretical plate is 2×105.

Expression to compute H from number of plates from is as follows:

  H=LN        (2)

Substitute 100 m for L and 2×105 for N in equation (2).

`

  H=(100 m2×105)(1000 mm1 m)=0.50 mm

Thus, plate height is 0.50 mm.

Value of Δtr is calculated as follows:

  Δtr=63.5 min63 min=0.5 min

Expression to compute resolution is as follows:

  Resolution=Δtrwavg        (3)

Substitute 0.5 min for Δtr, 0.384 min for wavg in equation (3).

  Resolution=0.5 min0.384min=1.3

Thus, value of resolution is 1.3.

(b)

Interpretation Introduction

Interpretation:

Extent of larger plate height has to be calculated and reason behind such massive plate height difference has to be calculated.

Concept Introduction:

Refer to part (a).

(b)

Expert Solution
Check Mark

Explanation of Solution

Ratio of plate height is calculated as follows:

  Plate height in liquid chromatographyPlate height in gas chromatography=(10 μm0.50 mm)(1 mm1000 μm)=150

Reason behind such massive plate height difference is that rate of longitudinal diffusion is much more rapid in gas than in liquid chromatography.

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