Chapter 26: Q34P (page 749)
Explain how neutral molecules can be separated by micellar electrokinetic chromatography. Why is this a form of chromatography? Why are micelles called a pseudostationary phase?
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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?
(a) The interstitial volume, , in Figure 26-15 is the volume at which the curves rise vertically at the left. Findfor the 25-nm-pore-size column. To the nearest order of magnitude, what is the smallest molecular mass of molecules excluded from this column? (b) What is the molecular mass of molecules eluted at 9.7 mL from the 12.5-nm column? (c)is the volume at which the curves drop vertically at the right. Find the largest molecular mass that can freely enter the 45-nm pores.
In ion-exclusion chromatography, ions are separated from nonelectrolytes by an ion-exchange column. Nonelectrolytes penetrate the stationary phase, whereas ions of the same charge as the resin are repelled by the fixed charges. Because co-ions have access to less of the column volume, electrolytes are eluted before nonelectrolytes. The chromatogram shows the separation of trichloroacetic acid (TCA,), dichloroacetic acid (DCA,), and monochloroacetic acid (MCA,) by passage through a cation-exchange resin eluted with 0.01 M HCl. Explain why the three acids are separated and why they emerge in the order shown.
The water-soluble vitamins niacinamide (a neutral com- pound), riboflavin (a neutral compound), niacin (an anion), and thiamine (a cation) were separated by micellar electrokinetic chromatography in 15mMborate buffer (pH8.0)with 50mMsodium dodecyl sulphate. The migration times were niacinamide (8.1min), riboflavin (13.0min), niacin (14.3min), and thiamine. What would the order have been in the absence of sodium dodecyl sulphate? Which compound is most soluble in the micelles?
26-B. Vanadyl sulfate , FM 163.00), as supplied commercially, is contaminated withandA solution was prepared by dissolving 0.2447g of impurein 50.0 mL of water. Spectrophotometric analysis indicated that the concentration of the blueion was 0.0243M. A 5.00-mL sample was passed through a cation-exchange column loaded with. Whenfrom the 5.00-mL sample became bound to the column, thereleased required 13.03mL of 0.02274M NaOH for titration. Find the weight percent of each component) in the vanadyl sulfate.
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