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Chapter 26: Q11 P (page 747)

(a) Explain how anions and cations can be separated by hydrophilic interaction chromatography in Figure 25-4, using the zwitterion stationary phase in Figure 25-16. Why does the gradient go from CH3CN.CH3CNto lowcontent?

(b) Explain how the charged aerosol detector used in Figure 26-4 works.

Short Answer

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We will explain the following in this solution:

  1. How cations and anions can be separated by hydrophilic interaction chromatography from figure 26-4 while using the zwitterion stationary phase in figure 25-16.
  2. How the charged aerosol detector used in figure 26-4 works.

Step by step solution

01

Definition of zwitterion

  1. The stationary phase is hydrophilic with positive and negative charges being fixed in a zwitterion.
02

Hydrophilic interaction chromatography

  • The stationary phase is polar with a layer of aqueous phase on surface.
  • The solvent is made more polar than the stationary phase, so it could elute the polar solutes.
  • when acetonitrile concentration is decreased eluent strength + eluent polarity increases.
03

Functions of charged aerosol detector

b. Nebulized effluent aerosol gains charge which is proportional to mass (nonvolatile)

  • Fraction of aqueous phase increases; as a result the eluent strength and polarity are increased.
  • 20% acetonitrile + 80% aqueous buffer eluent strength is high, so both ions are eluted quickly (ions cannot be separated due to rapid elution).
  • 40% acetonitrile + 60% aqueous buffer eluent strength being lower, so both ions are eluted slowly (ions are selectively separated).

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Most popular questions from this chapter

(a) How many moles of analyte are present in a60.0cm×25μmsolution that occupies 1.0% of the length of a60.0cm×25μmcapillary?(b) What voltage is required to inject this many moles into a capillary in 4.0 s if the sample has 1/10 of the conductivity of background electrolyte,μmp=3.0×10-8m2/(V×s) and the sample concentration is10.0μM?

26-D. Consider a capillary electrophoresis experiment conducted near pH9, at which the electroosmotic flow is stronger than the electrophoretic flow.

(a) Draw a picture of the capillary, showing the placement of the anode, cathode, injector, and detector. Show the direction of electroosmotic flow and the direction of electrophoretic flow of a cation and an anion. Show the direction of net flow.

(b) Using Table 15-1, explain why CI-has a shorter migration time than I-Predict whether Br-will have a shorter migration time than CI-or a greater migration time than I-

(c) Why is the mobility of I-greater than that ofCI-?

Would molecular exclusion, affinity, or hydrophobic interaction chromatography be most appropriate for each of the following applications?

  1. Purifying and concentrating a crude mixture of an antibody.
  2. Desalting a solution containing a 30kDa protein.
  3. Finding the molecular mass distribution of polystyrene with 15kDa average mass.
  4. Separation of cytochrome c (12 400 Da) and ribonuclease A (12 600 Da). Cytochrome c has lower surface hydrophobicity than ribonuclease A.

Electrophoretic mobility of the anionic form A2 of the weak acid phenol (HA=C6H5OH)and its derivatives are:

(a) Explain the trend in electrophoretic mobility from phenol to 4-methylphenol to 4-ethylphenol.

(b) Predict the electrophoretic mobility of the analytes at pH 10.0. Explain why the predicted mobility differs from mA2. (c) The electroosmotic mobility is toward the cathode and greater in magnitude than the analyte electrophoretic mobilities. In what order will the peaks appear in the electropherogram at pH 10.0?

Material balance. If you intend to measure all the anions and cations in an unknown, one sanity check on your results is that the total positive charge should equal the total negative charge. The table lists concentrations of anions and cations measured in pond water in an undergraduate experiment and expressed in mg/mL.

Find the total concentration of negative and positive charge (mol/L) to assess the quality of the analysis. What do you conclude about this analysis?
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