You wish to determine whether isocratic or gradient elution should be used for a

Question

You wish to determine whether isocratic or gradient elution should be used for a separation. For the initial run, a wide gradient from 5 vol% to 95 vol% B was used. For a 0.48 × 15 cm column containing 3-?m particles with a flow rate of 1.1 mL/min, what is the gradient time, tG, for this initial run? Assume S, the slope of the linear-solvent-strength model, is equal to 4.

You wish to determine whether isocratic or gradient elution should be used for a separation. For the initial run, a wide gradient from 5 vol% to 95 vol% B was used. For a 0.48 x15 cm column containing 3-um particles with a flow rate of 1.1 mL/min, what is the gradient time, tG, for this initial run? Assume S, the slope of the linear-solvent-strength model, is equal to 4. Number min Based on your initial results, you decided that using a would be appropriate for your You optimized the gradient from 19 vol% 32 vol% min flow rate of 1.1 mL/min. Calculate the average retention factor, k for this optimized separation. Number

Explanation / Answer

We know that

Gs = Vm X wide gradient / F X tg

Vm = Volume = pi X r^2 X L = 3.14 X 0.48 X 0.48 X 15 cm^3 = 10.85 cm^3

wide gradient for 90-955 = 90

F = flow rate = 1.1 mL / min = 1.1 cm^3 / min

tg= ?

Gs = 4

Putting values

tg = Vm X wide gradient / F X Gs = 10.85 X 0.90 / 1.1 X 4 = 2.21 minutes

2) K* = tg X F / %B range X Vm X S

S = slope= 4

K* = 10.7 X 1.1 / 0.13 X 10.85 X 5 = 1.67

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