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Chapter 25: Q7P (page 707)
If along HPCL column has a place height of 5.0 what will be the half-width (in seconds) of a peak eluted at 10.0min? if plate height,what will be?
The half-width (in seconds) of a peak eluted.
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A mixture of 14compounds was subjected to a reversed-phase gradient separation going from 5%to 100%acetonitrile with
a gradient time of 60min. The sample was injected at t =time. All peaks were eluted between 22and 50min.
(a) Is the mixture more suitable for isocratic or gradient elution?
(b) If the next run is a gradient, select the starting and ending %acetonitrile
and the gradient time.
(a) Nonpolar aromatic compounds were separated by HPLC on an octadecylbonded phase. The eluent was 65 vol% methanol in water. How would the retention times be affected if 90% methanol were used instead?
(b) Octanoic acid and 1-aminooctane were passed through the same column described in (a), using an eluent of 20% methanol/80% buffer (pH 3.0). State which compound is expected to be eluted first and why.
role="math" localid="1656416023291"
(c) Polar solutes were separated by hydrophilic interaction chromatography (HILIC) with a strongly polar bonded phase. How would retention times be affected if eluent were changed from 80 vol% to 90 vol% acetonitrile in water?
(d) Polar solutes were separated by normal-phase chromatographyon bare silica using methyl t-butyl ether and 2-propanol solvent. How would retention times be affected if eluent were changed from 40 vol% to 60 vol% 2-propanol? (Hint: See Table 25-4.)
25-2Why does the retention onder of peaks 2 and 3 change on the polar embedded column?
a) UHPLC can provide exquisite resolution when run slowly on long columns or rapid separation with reasonaple resolution if short columns are run fast. the drug acetaminophern run on a UHPLC column has a retention time of min and a width at half-height of .Find the plate number and plate height. How many diameter particles places placed dide-by are equal to one theoretical plate?
b) From figure,we expect an optimum plate height of how many particles placed side-by- side are equal to one theroretical plate? Do you think the column in (a) is being run for maximum resolution or maximum speed?
In monolithic columns60 the stationary phase is a single porous piece of silica or polymer filling the entire column and synthesized within the column from liquid precursors. Monolithic columns offer similar plate height to HPLC particles, but with less resistance to flow. Therefore, faster flow or longer columns can be used. The figure shows separation of isotopic molecules on a long monolithic column. Packed columns have too much resistance to flow to be made so long.
Separation of isotopic molecules on a 440-cm-long monolithic C18-silica column eluted with(30: 70 vol/vol) at 308C. [Data from K. Miyamoto, T. Hara, H. Kobayashi, H. Morisaka, D. Tokuda, K. Horie, K. Koduki, S. Makino, O. Nu帽ez, C. Yang, T. Kawabe, T. Ikegami, H. Takubo, Y. Ishihama, and N. Tanaka, 鈥淗igh-Efficiency Liquid Chromatographic Separation Utilizing Long Monolithic Silica Capillary Columns,鈥� Anal. Chem. 2008, 80, 8741.]
(a) Unretained thiourea is eluted in 41.7 min. Find the linear velocity ux (mm/s).
(b) Find the retention factor k for
(c) Find the plate number N and plate height for
(d) Assuming that the peak widths forand are the same as that of , find the resolution of and .
(f) If we just increased the column length to increase N, what value of N and what column length would be required for a resolution of 1.000?
(g) Without increasing the length of the column, and without changing the stationary phase, how might you improve the resolution?
(h) When the solvent was changed from(30:70 vol/vol) to(10:5:85), the relative retention for C6H5D andincreased to 1.0088 and the retention factor for C6H6 changed to 17.0. If the plate number were unchanged, what would be the resolution?
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