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Chapter 25: Q4P (page 707)

a. Why is high pressure needed in HPLC?

b. For a given column length , why do smaller particles give a higher plate number?

c. What is bonded phase in liquid chromatography?

Short Answer

Expert verified

The high pressure in HPLC is needed for usable flow rate.

Smaller particles have a higher plate number because the optimum flow rate for smaller particles is faster because the distance through which the solute must diffuse is shorter.

A bonded stationary phase is covalently attached to the surface.

Step by step solution

01

Step 1:Explanation

For the part (a), the high pressure in HPLC is needed for usable flow rate.

For the part (b), the Smaller particles have a higher plate number because the optimum flow rate is faster because the distance through which the solute must diffuse is shorter.

02

Explanation

For the part (c), a bonded stationary phase is covalently attached to the surface. For an example, silica.

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Most popular questions from this chapter

HPLC peak should generally not have an asymmetry factor, B/A in figure 23-14,outside the range0.9-1.5

  1. Sketch the shape of a peak with an asymmetry of 1.8
  2. What might you do to correct the asymmetry?

what are criteria for an adequate isocratic chromatographic separation?

Two peaks emerge from a reversed-phase chromatography column as sketched in the illustration.

According to Equation 23-33, resolution is given by

Resolution=N4(伪-1)伪(k21+k2)

where Nis plate number, 伪is relative retention (Equation23-20), and k2 is the retention factor for the more retained component (Equation 23-16).

(a) If you decrease the amount of organic solvent in the mobile phase, you will increase retention. Sketch the chromatogram if retention factors increase but Nand 伪are constant.

(b) If you change the solvent type or the stationary phase, you will change the relative retention. Sketch the chromatogram if伪increases but Nandk1are constant.

(c) If you decrease particle size or increase column length, you can increase the plate number. Sketch the chromatogram if Nincreases by (i) decreasing particle size and (ii) increasing column length. Assume 伪and k2are constant.

Retention factors for three solutes separated on aC8non-polar stationary phase are listed in the table. Eluent was a 70 : 30 (vol/vol) mixture of 50 mM citrate buffer (adjusted to pH withNH3) plus methanol. Draw the dominant species of each compound at each pH in the table and explain the behavior of the retention factors.

To which kinds of analytes do these liquid chromatography detectors respond?

(a) ultraviolet

(b) refractive index

(c) evaporative light scattering

(d) charged aerosol

(e) electrochemical

(f) fluorescence

(g) nitrogen chemiluminescence

(h) conductivity
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