Chapter 26: Q7P (page 746)
What is deionized water? What kind of impurities are not removed by deionization?
Deionized water:Water that has passed through ion-exchangers to convert the present cations to protons and present anions to hydroxides
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Figure 26-24 shows the effect on resolution of increasing voltage from 28 to120kV.
(a) What is the expected ratio of migration times in the two experiments? Measure the migration times for peak 1 and find the observed ratio.
(b) What is the expected ratio of plates in the two experiments?
(c) What is the expected ratio of bandwidths?
(d) What is the physical reason why increasing voltage decreases bandwidth and increases resolution?
Blue Dextran 2000 was eluted during gel filtration in a volume of 36.4mL from a 40 * 2cm (length diameter) column of Sephadex G-50, which fractionates molecules in the molecular mass range 1500-30000.
(a) At what retention volume would hemoglobin (molecular mass 64000 ) be expected?
(b) Suppose that radioactive, which is not adsorbed on the column, is eluted in a volume of 109.8 mL. What would be the retention volume of a molecule with Kav= 0.65?
To obtain the best separation of two weak acids in capillary electrophoresis, it makes sense to use the pH at which their charge difference is greatest. Prepare a spreadsheet to examine the charges of malonic and phthalic acid as a function of pH. At what pH is the difference greatest?
Decomposition of dithionite.was studied by chromatography on an anion-exchange column eluted with 20mM tri-sodium 1, 3, 6-napthalenetrisulfonate in 90 vol%
vol%with ultraviolet detection at 280 nm. A solution of sodium dithionite stored for 34 days in the absence of air gave five peaks identified asAll the peaks had a negative absorbance. Explain why.
Electrophoretic mobility of the anionic form A2 of the weak acid phenol 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?
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