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Chapter 23: Q34P (page 631)

Why does plate height depend on linear velocity, not volume flow rate?

Short Answer

Expert verified

The solution is

the longitudinal diffusion (Bux) is inversely proportional to the duration the solute spends on the column (ux).

Step by step solution

01

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We'll explain why plate height is affected by linear velocity but not by volume flow rate in this work.

02

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Volume flow rate

- for example,1mLmin ; indicates how many mL of solvent pass through the column per minute.

Flow rate that is linear.

- For example,1cmmin tells us how many cm the solvent travels per minute.

03

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As a result, linear flow rate defines how complete the two-phase equilibrium is:

- the van Deemter equation is used to calculate the value of equilibration time (mass transfer).

- furthermore, the longitudinal diffusion (Bux)is inversely proportional to the duration the solute spends on the column (ux).

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Most popular questions from this chapter

A Gas chromatogram of a mixture of toluene and ethyl acetate is shown here:

(a)Use the width of each peak (measured at the base)to calculate the number of theoretical plates in the column. Estimate all lengths to the nearest 0.1 mm.

(b)Using the width of the toluene peak at its base, calculate the width expected at half height. Compare the measured and calculated values. When the thickness of the the line is significant relative to the length being measured, it is important to take the pen line width into account. You can measure from the edge of one line to the corresponding edge of the other line,as shown here.

A chromatographic procedure separatesof unknown mixture on a column with a length ofand a diameter of. (a) What size column would you use to separateof the same mixture? (b) If the flow ison the small column, what volume flow rate should be used on the large column? (c) The mobile phase occupiesof the column volume. Calculate the linear velocity for the small column and the large column.

For the separation of A and B by column 2 in Problem 23-32:

(a) If broadening is mainly due to longitudinal diffusion, how should the flow rate be changed to improve the resolution?

(b) If broadening is mainly due to the finite equilibrium time, how should the flow rate be changed to improve the resolution?

(c) If broadening is mainly due to multiple flow paths, what effect will flow rate have on the resolution?

Why is the extraction of a metal ion into an organic solvent with more complete at higher ?

23-41. Describe how nonlinear partition isotherms lead to non-Gaussian band shapes. Draw the chromatographic peak shapes produced by an overloaded gas chromatography column and an overloaded liquid chromatography column.
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