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Chapter 23: Q37P (page 631)

In chromatography, why is the optimal flow rate greater if the stationary phase particle size is smaller?

Short Answer

Expert verified

The solution is

the smaller the particle, the faster the equilibrium between the stationary and mobile phases is achieved.

Step by step solution

01

of 3

In this job, we will explain why the ideal flow rate in chromatography is higher when the stationary phase particle size is lower.

02

of 3

Representative diffusion coefficients at 289K are shown in Table 23-1:

- As the size of the diffusing particle and the viscosity of the fluid both rise, the friction coefficient increases.

- Some larger molecules diffuse slower than small ones due to their vast radius.

03

of 3

As a result, the smaller the particle, the faster the equilibrium between the stationary and mobile phases is achieved.

- As seen in Table 23-1, tiny molecules have a greater diffusion coefficient.

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Most popular questions from this chapter

23-42. A separation of 2.5mgof an unknown mixture has been optimized on a column of length L and diameter d .

(a) Explain why you might not achieve the same resolution if the 2.5mgof unknown mixture were injected in twice the injection volume.

(b) Explain why you might not achieve the same resolution if5.0mg of unknown mixture were injected in the original injection volume.

Consider a chromatography column in whichVs=Vm/5 Find the retention factor if K = 3 and if K = 30 .

Isotopic compounds (isotopologues) are separated in Figure 23-15 by repeated passage through a pair of columns. Each cycle in the figure represents

one pass through length L = 25 cm containing

L theoretical plates. The relative retention (α) is and the retention factor for

L-phenylalanine is k2=1.62. (a) The observed resolution after 10 cycles is 1.60 .

Calculate the number of theoretical plates, N , in column length L . The mixture

has passed through length 10L in 10 cycles.

(b) Find the plate height in μm.

(c) Predict the resolution expected from two cycles. The observed value is 0.71 .

(a) Write the meaning of the retention factor,k, in terms of time spent by solute in each phase. (b) Write an expression in terms of kfor the fraction of time spent by a solute molecule in the mobile phase. (c) The retention ratio in chromatography is defined as R=timeforsolventtimeforsolutetopassthroughcolumn=tmtrShow that is related to the retention factor by the equation R=1/k+1

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

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