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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.

Match statements 1鈥�5 with the band broadening terms in the second list.

1. Depends on radius of open tubular column.

2. Not present in an open tubular column.

3. Depends on length and radius of connecting tubing.

4. Increases with diffusion coefficient of solute.

5. Increases with thickness of stationary phase film.

A Multiple paths

B Longitudinal diffusion

Cm Equilibration time in mobile phase

Cs Equilibration time in stationary phase

EC Extra column band broadening

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

For a given value of [HL]orgin Equation 23-13, over what pH range (how many pH units) will D change from if n = 2?

A chromatographic procedure separatesof unknown mixture on a column with a length of 40cmand a diameter of 0.85cm . (a) What size column would you use to separate 100mgof the same mixture? (b) If the flow is 0.22mL/minon the small column, what volume flow rate should be used on the large column? (c) The mobile phase occupies 35%of the column volume. Calculate the linear velocity for the small column and the large column.
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