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Chapter 26: Q38P (page 749)

(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.

Short Answer

Expert verified

a)maleate will have a greater electrophoretic mobility than fumarate.

b)At pH=4.0 the maleate is the faster molecule and would be eluted first considering that anions move faster than the endosmotic flow.

Step by step solution

01

Step 1:Predict whether fumarate or maleate will have greater electrophoretic mobility

a)From picture in the task we can see that fumerate has a longer chain than maleate,so that fumerate has a greater frictional coefficient


Considering that both molecules have the same charge,we can say that maleate will have a greater electrophoretic mobility than fumarate.

02

Step 2:Predict the order of elution of these two species

In this case maleate would move faster upstream than fumarate,so fumarate would be eluted first.

03

Step 3:At pH=4.0 we will predict the order of elution

At pH=4.0 the maleate is the faster molecule and would be eluted first considering that anions move faster than the endosmotic flow.

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Most popular questions from this chapter

What is the effect on injection time if you decrease the applied voltage by a factor of 2?

State three different methods to reduce electroosmotic flow. Why does the direction of electroosmotic flow change when a silica capillary is washed with a cationic surfactant?

Norepinephrine (NE) in human urine can be assayed by ion-pair chromatography by using an octadecylsilane stationary phase and sodium octyl sulfate as the mobile-phase additive. Electrochemical detection (oxidation at 0.65 V versus Ag|AgCl) is used, with 2,3-dihydroxybenzylamine (DHBA) as internal standard.

  1. Explain the physical mechanism by which an ion-pair separation works.
  2. A urine sample containing an unknown amount of NE and a fixed, added concentration of DHBA gave a detector peak height ratio NE/DHAB = 0.298. Then small standard additions of NE were made, with the following results:

  3. Added concentration of NE ( ng/mL )

    Peak height ratio NE/DHBA

    12

    0.414

    24

    0.554

    36

    0.664

    48

    0.792

  • Use the graphical treatment in Section 5-3, find the original concentration of NE in the specimen.

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 (9.8m/s2). 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?

The migration time for Cl-in a capillary zone electrophoresis experiment is 17.12 min and the migration time for l-is 17.78 min. From mobilities in Table 15-1, predict the migration time of Br(The observed value is 19.6 min.)

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