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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?
The solution is
the smaller the particle, the faster the equilibrium between the stationary and mobile phases is achieved.
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The theoretical limit for extracting solute Sfrom into phase2 is attained by dividing into an infinite number of infinitesimally small portions and conducting an infinite number of extractions. With a partition coefficient, the limiting fraction of solute remaining in phase . Let volume be divided intoequal portions to conduct extractions. Find the fraction of S extracted into phase 2 for n = 1,2, and 10extractions. How many portions are required to attain 95%of the theoretical limit?
The weak base equilibrates between water (phase 1) and benzene (phase 2)
(a) Define the distribution coefficient, D for this system.
(b) Explain the difference between D and K the partition coefficient.
(c) Calculate D at
(d) Will D be greater or less at ? Explain why.
The three chromatograms shown here obtained with 2.5, 1.0 and 0.4 of ethyl acetate injected on the same column under the same conditions. Explain why the peak becomes less symmetrical with increasing sample size.
(a) For the asymmetric chromatogram in Figure 23-14, calculate the asymmetry factor, .(b) The asymmetric chromatogram in Figure 23-14 has a retention time equal to 15.0 min and a of 44s . Find the number of theoretical plates. (c) The width of a Gaussian peak at a height equal to of the peak height is . Suppose that the peak in (b) is symmetric with . Use Equations 23-30 and 23-32 to find the plate number.
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.
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