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Chapter 26: Q42P (page 749)
Measure the width of the peak at half-height in Figure 26-32 and calculate the plate number. The capillary length to detector was 40.0 cm. Find the plate height.
The plate number and plate height
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Would molecular exclusion, affinity, or hydrophobic interaction chromatography be most appropriate for each of the following applications?
Figure 26-23 shows the separation of substituted benzoates. There is a peak of unknown identity at 86.0 seconds. (a) Is the unknown a cation, neutral, or an anion? (b) Find the apparent mobility and electrophoretic mobility of the unknown peak.
Ferritin (molecular mass 450 000), transferrin (molecular mass 80 000), and ferric citrate were separated by molecular exclusion chromatography on Bio-Gel P-300. The column had a length of 37 cm and a 1.5-cm diameter. Eluate fractions of 0.65 mL were collected. The maximum of each peak came at the following fractions: ferritin, 22; transferrin, 32; and ferric citrate, 84. (That is, the ferritin peak came at an elution volume of 22 3 0.65 5 14.3 mL)Assuming that ferritin is eluted at the interstitial volume and that ferric citrate is eluted at , findfor transferrin.
(a) A long thin molecule has a greater friction coefficient than a short fat molecule. Predict whether fumarate or maleate will have greater electrophoretic mobility.
(b) Electrophoresis is run with the injection end positive and the detection end negative. At pH 8.5, both anions have a charge of 22.The electroosmotic fl ow from the positive terminal to the negative terminal is greater than the electrophoretic flow, so these two anions have a net migration from the positive to the negative end of the capillary in electrophoresis. From your answer to part (a), predict the order of elution of these two species. (c)At pH 4.0, both anions have a charge close to 21, and the electroosmotic fl ow is weak. Therefore electrophoresis is run with the injection end negative and the detection end positive. The anions migrate from the negative end of the capillary to the positive end.Predict the order of elution.
Injection in some homebuilt capillary electrophoresis instruments is performed by raising the sample vial to create a siphon. The pressure exerted by a column of water of heightiswhereis the density of water and gis the acceleration of gravity (). To what height would you need to raise the sample vial to create the necessary pressure to load the sample in 4.0 s? Is it possible to raise the inlet of this column to this height? How could you obtain the desired pressure?
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