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Chapter 25: Q35P (page 710)

The “rule of three” states that the retention factor for a given solute decreases approximately threefold when the organic phase increases by10%.In figure 25-12,tm=2.7min. Find k for peak 5at 40%B .predict the retention time for peak at B and compare the observed and predicted times.

Short Answer

Expert verified

The rule of three states that the retention factor for a given solute decreases.

K=tr-tmtmk=11-27min2.7mintr=27.81min

Step by step solution

01

Definition of retention

Retention implies the maintenance, possession, control, or retention of moisture.

According to the figure 25-12, we see that retention time for peak 5 is 11 min (for 50% B). So, the retention factor is

K=tr-tmtmk=11-27min2.7mink=3.1

02

Rule of three

Then, when B is 40%, k is (according to the rule of three) given by

k=3⋅3.1=9.3

Retention time is

tr=k.tm+tmtr=9.3.2.7min+2.7mintr=27.81min

According to the figure 25-12, the observed retention time is 20.2 min.

Hencetr=27.81min.

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Most popular questions from this chapter

A bonded stationary phase for the separation of optical isomers has the structure

To resolve the enantiomers of amines, alcohols, or thiols, the compounds are first derivatized with a nitroaromatic group that increases their interaction with the bonded phase and makes them observable with a spectrophotometric detector.

When the mixture is eluted with 20 vol% 2-propanol in hexane, the (R)-enantiomer is eluted before the (S)-enantiomer, with the following chromatographic parameters:

Resolution=Δtrwav=7.7

Relative retention(α)=4.53

k for (R)-isomer =1.35

tm=1.00min

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(c) The area of a Gaussian peak is1.064×peakheight×w1/2. Given that the areas under the two bands should be equal, find the relative peak heights(heightR//heightS).

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(a) Estimate the volume,Vm, and time,tm, at which unretained solute would emerge from each column. The observed times are 0.65 min for column A and 0.50 min for column B.

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(e) From Equation 25-12 in Box 25-4, estimate k* on Column B assuming S = 4 and withtm5 0.50 min.

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(b). Explain why the van Deemter curve for 1.8μmparticles in figure 25-3is nearly flat at high flow rate.what can you say about each of the terms in the van Deemeter equation for 1.8μmparticles.

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