Chapter 25, Problem 25.42P

a)

Interpretation Introduction

Interpretation:

The most suitable elution (gradient or isocratic) for the mixture has to be identified.

Concept introduction:

Running a broad gradient helps us to decide whether to use gradient elution or isocratic elution.  This can be decided by the gradient time and the retention time difference.

Gradient time is denoted by $t_G$ and this is the time over which is required to change the solvent composition.  The difference in retention time is denoted by $\Delta t$ and this is for the first and last peak obtained in chromatogram.

Two conditions are possible by considering the gradient time and retention time difference.  This can be given as shown below,

$\begin{array}{l}\Delta t/t_G>0.40-\text{Gradient Elution}\\ \Delta t/t_G<0.25-\text{Isocratic Elution}\\ 0.25<\Delta t/t_G<0.40-\text{Gradient or Isocratic elution}\end{array}$

Simply to say if all the peaks are eluted over a very narrow solvent range means, the feasible one is isocratic elution.  If a wide range of solvent is required means then the practical one that is possible is gradient elution.

b)

Interpretation Introduction

Interpretation:

The starting and ending percentage of Acetonitrile and gradient time has to be given.

Concept introduction:

Running a broad gradient helps us to decide whether to use gradient elution or isocratic elution.  This can be decided by the gradient time and the retention time difference.

Gradient time is denoted by $t_G$ and this is the time over which is required to change the solvent composition.  The difference in retention time is denoted by $\Delta t$ and this is for the first and last peak obtained in chromatogram.

Two conditions are possible by considering the gradient time and retention time difference.  This can be given as shown below,

$\begin{array}{l}\Delta t/t_G>0.40-\text{Gradient Elution}\\ \Delta t/t_G<0.25-\text{Isocratic Elution}\\ 0.25<\Delta t/t_G<0.40-\text{Gradient or Isocratic elution}\end{array}$

Simply to say if all the peaks are eluted over a very narrow solvent range means, the feasible one is isocratic elution.  If a wide range of solvent is required means then the practical one that is possible is gradient elution.