a. UHPLC can provide exquisite resolution when run on long columns at high pressure or rapid separations with reasonable resolution if short columns are run fast. The drug acetaminophen run on a 50x2.1 mmC18 50x2.1 mmC₁₈ is UHPLC column has a retention time of 0.63 min 0.63 min and a full width at half-height of 2.3 s. 2.3 s. Find the plate number and plate height. How many 1.7-μm-diameter 1.7-μm-diameter particles placed side-by-side are equal to one theoretical plate?

b. From Figure 25-3, we expect an optimum plate height of 4μm. 4μm. hi How many particles placed side-by-side are equal to one theoretical plate? Do you think the column in (a) is being run for maximum resolution or maximum speed?

Figure 25-3

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Plate height (um) 18 16 14 12 10 8 6 4 2 0 2 5 μm 3.5 μm 2.7 μm Superficially porous 1.8 μm 6 Linear velocity (mm/s) Harris/Lucy, Quantitative Chemical Analysis, 10e, Ⓒ 2020 W. H. Freeman and Company 8 10 at 24°C 24°C. FIGURE 25-3 van Deemter curves: Plate height as a function of linear velocity (mm/s) (mm/s) for microporous (Figure 25-5) stationary phase particle diameters of 5.0,5 05.0, 3.5,3.5, and 1.8 μm, 1.8 411, as well as superficially porous particles (Figure 25-9) with a diameter of 2.7 um 2.7 μm (0.5-um0.5-um porous layer thickness). Measurements for naphthalene eluted from C18-silica C18-silica (50 mm long-4.6 mm) (50 mm long x 4.6 mm) diameter with 60 vol% acetonitrile/40 vol% H20 60 vol% acetonitrile/40 vol% H₂O