CHEMISTRY 133

Spring, 2017 Homework Set 3

Only Additional Problems are Submitted for Grading

Set 3.1 - Complete for quiz on May 4^th

(New due date for Additional Problems = 5/9)

Ch. 22: 2, 7a, 17, 19, 22, 24, 26, 28, 31, 32, 38, 42, 43

Additional Problem 3.1 The table below shows the retention times and peak widths for 3 compounds separated by reversed-phase HPLC using a 250 mm length x 4.6 mm inside diameter column with an eluent of 45% acetonitrile, 55% water:

Compound	Retention time (min.)	Peak Width at half height (min.)	pKa
phenol	4.72	0.21	9.98
2-nitrophenol	5.68	0.25	8.39
2-methylphenol	5.91	0.26	10.09

Note: w_b = 1.70*w_1/2

a) If the flow rate is 1.00 mL/min and the column is 62% by volume packing material (including stationary phase), calculate the time it takes for mobile phase to flow through the column.

b) Calculate the retention factor for phenol.

c) Calculate the plate number for the column using the last eluting compound.

d) Calculate the resolution for the two least well-resolved peaks.

e) Calculate the relative retention (a) for the two least well-resolved peaks.

f) If the solvent is changed to an eluent of 45% acetonitrile, 55% pH = 8 buffer (about the maximum possible), what will happen to each retention time. You can assume that anions are unretained

Additional Problem 3.2. A gas bubble meter is used to determine the flow rate for a 0.32 mm (open tubular), 30 m column. If the column effluent takes 136 s for a bubble to travel 10.0 mL in the meter, calculate:

a) the flow rate at the bubble meter (mL/min)

b) the linear velocity (m/s)

c) the time expected for unretained solute to elute

For this question, you can ignore changes in temperature and pressure as the gas flows through the column (as well as any fraction of the bubble meter made up of water vapor).

Set 3.2 – Complete by May 11^th

Ch. 23: 3a, 5, 17,