# 25-5. (a) Use Equation 25-1 to estimate the length of column required to achieve 1.0 X 10 plates if the stationary phase particle size is 10.0, 5.0, 3.0, or 1.5 um. (b) If the retention time was 20 min on the 10.0-um-particle-size column, what is the retention time on the 5.0-, 3.0-, and 1.5-um columns from part (a)? Assume that flow rate is constant for all columns. (c) Use Equation 25-2 to estimate the pressure of the columns in (a) given that the pressure of the 10.0-uum column was 4.4 MPa. (d) If the flow rate was 2.0 mL/min, what is the baseline width (in time and volume) for the peaks on 10.0.5.0-, 3.0-, or 1.5-um col- umns from part (a)? (e) Which of these column configurations would require a UHPLC instrument? 3 000. L(cm) d. (um) (25-1) un Column pressure: P=122 (25-2) where u, is volume flow rate, is the viscosity of the solvent, L is the length of the column ris column radius, and do is the particle diameter. The factor f depends on particle shape and particle packing. The physical significance of Equation 25-2 is that pressure in HPLC is pro-

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