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Chapter 23: QDE (page 628)

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.

Short Answer

Expert verified

(a)Number of plates, N = 732 for ethyl acetate and 1036 for toluene.

(b)Calculated width at half height = 4.87mm.

Step by step solution

01

Step :1   

Finding the value of N (no. of plates) :

(a)For ethyl acetate, I measure tr=20.3mmand w=3.0mm(You will have measure different numbers depending on the size in your book)

We know that N=16tr2w2

Or,N=16脳20.323.02=732 plates

For toluene, I measuretr=66.8mm and w=8.3mm (You will have measure different numbers depending on the size in your book)

鈭� N=16脳66.828.32=1036 plates

02

Finding the value of width at half height :

(b) For toluene

Again Width at half height, w12=2.354w Or, w12=2.354脳8.3=4.87mm

The measured value of width at half height is in good agreement with the calculated value.

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Most popular questions from this chapter

An open tubular column is 30.01 mlong and has an inner diameter of 0.530mm. It is coated on the inside wall with a layer of stationary phase that is3.1渭尘thick. Unretained solute passes through in 2.16min, whereas a particular solute has a retention time of 17.32min. (a) Find the linear velocity and volume flow rate. (b) Find the retention factor for the solute and the fraction of time spent in the stationary phase.(c) Find the partition coefficient, K 5 cs/cm, for this solute.

23-1.If you are extracting a substance from water into ether, is it more effective to do one extraction with of ether or three extractions with ?

Solute S has a partition coefficient of 4.0 between water (phase 1) and chloroform (phase 2) in Equation 23-1.

(a) Calculate the concentration of in chloroform if[S]aqis 0.020M.

(b) If the volume of water is 80.0 mL and the volume of chloroform is 10.0 mL, find the quotient localid="1654852656619" (molSinchloroform)(molSinwater).

Two compounds with partition coefficients of 15 and 18 are to be

separated on a column with Vmi/Vs=3.0and localid="1654950413291" tm=1.0min. Calculate the

number of theoretical plates needed to produce a resolution of 1.5 .

23-32. Chromatograms of compounds A and B were obtained at the same flow rate with two columns of equal length. The value of tmis 1.3m in both cases.


(a) Which column has more theoretical plates?

(b) Which column has a larger plate height?

(c) Which column gives higher resolution?

(d) Which column gives a greater relative retention?

(e) Which compound has a higher retention factor?

(f) Which compound has a greater partition coefficient?

(g) What is the numerical value of the retention factor of peak A?

(h) What is the numerical value of the retention factor of peak B?

(i) What is the numerical value of the relative retention?
See all solutions

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